The shape, size, colour and texture of butterfly eggs varies greatly from one species to another. Eggs of Satyrines and Heliconiines are typically domed or barrel-shaped, adorned with between 8-30 vertical ribs, between which can be seen dozens of lateral ridges. Most Hesperiidae, Papilionidae and Riodinidae produce smooth globular eggs. The eggs of Polyommatines have a finely reticulated surface, and are shaped like flattened do-nuts. Pierines produce tall skittle-shaped eggs, with fine vertical ribbing.

All butterfly eggs have a depression at the top, in the centre of which is a hole called the micropyle, through which sperm enters during fertilisation.

The egg shell also is peppered with thousands of microscopic pores called aeropyles. Microscopic examination of the eggs of Riodinidae, Lycaenidae and Limenitidinae species reveals them to be adorned with hundreds of minute hexagonal pits. Tiny hollow spines emerge at the intersections of each hexagon. These are also aeropyles, and act as breathing tubes for the developing larva.

Thecla betulae egg details – Adrian Hoskins

Fertilisation

In the case of Nymphalidae and most other butterflies the eggs are already formed within the body of females when they emerge. They grow in size over a period of 2 or 3 days as they mature within the female’s abdomen.

Egg-laying is triggered when they reach a certain size, at which time they pass from the ovariole to the egg chamber. They are fertilised just prior to egg-laying, the male’s sperm having been stored until this time within a receptacle in the female abdomen.

Oviposition

Butterflies lay their eggs either singly or in batches, on or near the foodplants that will be used by the caterpillars. Many species lay their eggs away from the foodplant, on dry grass stems, dead leaves or even on soil. This strategy prevents the eggs from being accidentally devoured by grazing animals. It also makes it more difficult for parasitoid wasps and flies to locate the eggs.

Some species, e.g. the Marbled White Melanargia galathea, drop their eggs randomly as they fly amongst tall grasses, but most species have very precise requirements. Pearl-bordered Fritillaries Clossiana euphrosyne for example lays their eggs singly on dead bracken or dry grass stems that are within a metre of their caterpillar’s foodplant, dog violet. The White-letter Hairstreak Satyrium w-album is even fussier, always laying it’s eggs on elm twigs, at the precise point where the new year’s growth and old growth meet.

Silver-washed Fritillaries Argynnis paphia lay their eggs in chinks on the bark of oak trees, but the larvae don’t eat oak – they begin by eating their own egg-shells, and then go into hibernation until the following spring, when they descend the tree trunks to feed on the leaves of nearby violets.

In the tropics eggs are often glued underneath the leaves of trees and bushes where they are protected from rain and from the desiccating effects of hot sunshine. In the Amazonian rainforests Heliconiine butterflies often lay their eggs on Passiflora tendrils, presumably to place them as far out of the reach of marauding ants as possible.

Orange tip caterpillars Anthocharis cardamines normally feed on cuckoo flower or garlic mustard leaves, but if they encounter another caterpillar they become cannibalistic. It would therefore be wasteful if more than one egg was laid on each plant, so the butterflies have evolved the ability to detect eggs that have already been laid by other females.

Studies have shown that many members of the subfamilies Pierinae, Heliconiinae, Danainae and Papilioninae have this ability, and avoid laying on plants carrying eggs laid by other members of their own genus or species.

Foodplant selection

The larvae of most species will only eat the leaves of one or two species of plant and will die if they find themselves on the wrong type of tree, bush or herb. Even oligophagous species – those that are able to feed on more than one type of plant – have a hierarchal order of foodplant preference, only accepting less nutritional species if they are unable to locate their preferred foodplant.

Butterflies therefore spend a great deal of time checking various leaves to ascertain whether they are of the correct species for egg-laying. Studies have shown that Heliconius, Battus, Colias and Perrhybris butterflies initially determine leaf choice by shape and size, but use taste and smell to confirm that the leaf is chemically “correct”. 

It is common to see butterflies flitting from plant to plant, alighting momentarily on leaves, tasting the foliage using olfactory sensors on their feet. All female butterflies have spines on the underside of their forelegs. When they land on a leaf these spines puncture the surface, releasing aromas that are detected by the olfactory sensors.

It isn’t just enough to locate the correct species of plant. The eggs usually have to be laid on tender young leaves or buds, as the older leaves often contain toxins that can kill them. They also have to be laid on plants that are growing in very precise conditions – just the right degree of shade, just the right conditions of temperature and humidity, and at a height on the plants where they will not get eaten by browsing herbivores.

Eggs are often laid on the tips of buds, usually quite high up on the tree or bush. This way they are less likely to be found by ants. Female butterflies often spend long periods probing about with the tips of their abdomens, being extremely careful about the positioning of each individual egg.

In Peru Perrhybris pyrrha females habitually alight on almost any available leaf except ferns when searching for the Capparis leaves on which they eventually oviposit. A female will reject several Capparis trees before selecting a particular one. Having found a tree that suits her she will then spend up to 30 minutes comparing dozens of leaves. She will settle on a leaf-tip, run up towards the base of the leaf as if measuring it, and then move on to another leaf.

Eventually she narrows her choice down to just two adjacent leaves and then spends several minutes skipping back and forth between them before finally deciding which leaf to oviposit on. If she is disturbed part way through the oviposition process she will flee up into the canopy, but will return a few minutes later, relocate the leaf and complete laying the egg batch.

The factors that induce a female to lay on a particular specimen of tree or bush, or on a particular leaf, are often a mystery to human observers. Gonepteryx rhamni always lays its eggs singly but I have counted up to 19 on a single leaf, and up to 100 on a tiny bush. These may have been laid by a single returning female or by several females in succession.

These figures pale into insignificance however when learning about observations of various Capparis feeding species – In Kenya in 1926 Somersen estimated that a single 1 metre high bush of Capparis held about 57,000 eggs and young larvae of Belenois aurota.

In Sydney, Australia during a mass migration of Caper Whites Anaphaeis java, Waterhouse estimated that about 250,000 eggs were laid on a single 5 metre high Caper tree!

Laying in batches

Butterflies usually lay the bulk of their eggs within the first few days of their lives. Older females lay smaller eggs, and the resulting caterpillars take longer to mature, making them more prone to predation and parasitism. This is probably part of the reason why Perrhybris and numerous other species avoid delay, and have evolved to lay all of their eggs in a single batch immediately after copulation. This strategy also ensures that as many eggs as possible are laid before the butterfly falls prey to a bird, reptile, wasp or spider.

egg batch under leaf, species unknown, Peru – Adrian Hoskins

Some species lay their egg batches in neat clusters like that shown above, while others including Aporia, Euphydryas, Chlosyne and Aglais produce untidy heaps in which the eggs are up to 3 layers deep. I have also seen cases where Euphydryas aurinia females have laid their eggs on top of an egg batch produced by another female of the same species.

Laying in batches improves the survival prospects for individual caterpillars. Wasps preferentially parasitize eggs at the edges of batches because they cannot easily reach those at the centre with their ovipositors. It seems that a few individual eggs around the edge of the batch are sacrificed to ensure that the bulk of them at the centre of the batch are left alone. Eggs at the centre are also less likely to be eaten by predatory insects, and are much better protected against desiccation.

As might be expected there are also negative factors involved when a butterfly “puts all it’s eggs in one basket” – an entire egg batch could be deliberately eaten by a bird, snail, reptile or amphibian; or accidentally consumed by a grazing animal. To reduce the likelihood of this happening butterflies choose their egg-laying sites with great care.

Several Nymphalidae genera including Hamadryas, Polygonia and Araschnia lay their eggs in long vertical strands, dangling from the underside of leaves. Hamadryas amphinome sometimes lays in strands of up to 15 eggs long. It is not known what advantage the butterflies gain by adopting this strategy – perhaps the eggs at the end of the string are less susceptible to leaf mould?

egg batch of Marsh Fritillary Euphydryas aurinia, Wiltshire, England – Adrian Hoskins

egg batch of Small Tortoiseshell Aglais urticae, Hampshire, England – Adrian Hoskins

Maturation

With many species of butterfly the eggs need to mature within the female for between 3-6 days before egg laying commences. Once this period has elapsed, oviposition activity is controlled at least partially by the butterfly’s inbuilt biological or “circadian” clock. Hence she will only lay her eggs at a particular time of day, during which her activities adhere to a “rest-feed-fly-oviposit” sequence.

This is triggered and modified by environmental cues such as temperature and light levels. The “oviposit” part of the sequence, often referred to simply as an egg-laying run, typically lasts for about 5 minutes, but can be shortened if cloud obscures the sun and lowers temperatures.

Incubation

The incubation period varies greatly from species to species. Eggs of tropical butterflies usually hatch within a week, but in temperate areas 10-14 days is more typical.

There are however many species, such as Purple Hairstreak Quercusia quercus, Chalkhill Blue Lysandra coridon and High Brown Fritillary Argynnis adippe, in which the eggs hibernate over winter, and in these cases the incubation period can last for several months.

Egg parasites

The eggs of butterflies and moths are valuable sources of protein. In addition to the threats from birds, snails, reptiles, amphibians and grazing mammals already mentioned, they are prone to parasitisation by microscopic wasps and flies. 

It may seem surprising that something as small as a butterfly egg has its own parasitoids, but these cause high losses. The main parasitoids are wasps in the families Scelionidae and Trichogrammidae – as many as 60 of these can emerge from a single butterfly egg !

Armature

Larvae in some subfamilies e.g. Satyrinae, Hesperiinae, Notodontinae, Noctuinae, Geometrinae and Sphinginae are normally devoid of hairs. Those in many other subfamilies including Lasiocampinae, Arctiinae, Lymantridae, Acronictinae and Hemileucinae bear hair-like setae. Sometimes these are sparse but in some species such as the ‘woolly bear’ Garden Tiger moth Arctia caja they are very long and dense, giving the larva a furry appearance.

The thick coat of hair makes it more difficult for a bird or reptile to swallow a larva. It also has the added bonus of cushioning it in the event of a fall. Additionally hair traps pockets of air around the caterpillar’s body, allowing it to survive if it has the misfortune to fall into a puddle. Caterpillars of Arctia caja for example can survive periods of several days submerged in water.

larva of Drinker moth Euthrix potatoria ( Lasiocampidae ), England – Adrian Hoskins

The hairs of moths in the families Lasiocampidae and Lymantridae often have irritating properties. In the case of the Drinker moth Euthrix potatoria they do little more than cause a mild itch, but the hairs shed by the larva of the Brown-tail moth Euproctis chrysorrhoea are rather more troublesome and can cause a severe rash on human skin. It is generally the case however that larvae from the temperate regions of the world are fairly safe to handle. In the tropics it is a very different story, and all hairy or spiky larvae should be treated with caution.

Caterpillar of Flannel moth ( Megalopygidae ), Peru © Adrian Hoskins

The larvae of moths in the family Megalopygidae look fluffy and almost invite you to handle them, but hidden beneath the soft hairs are a series of sharp spines. If the larvae are handled the spines break, releasing a chemical which causes excruciating pain.

Unidentified moth larva, Peruvian Andes © Adrian Hoskins

Many caterpillars, such as the unidentified species illustrated above, use bright patterns and colours to warn enemies that they are distasteful or poisonous. Others including those of the Nymphalinae, Heliconiinae, Limacodidae and Saturniidae are armed with rows of extraordinary multi-branched spikes and horns. These are enough to deter many birds from attacking, and no doubt also offer a degree of protection against wasps, ants and other insect predators.

Lexias pardalis, West Malaysia – Gan Cheong Weei

Brenthis daphne, Hungary – Peter Bruce-Jones

Spikes, hairs and other armature are most pronounced in young larvae which feed communally, so it seems likely that one of their functions may be to protect them against cannibalism.

In most species the spines are harmless or cause only mild irritation in humans, but in at least one Saturniidae species they can inflict a potentially lethal sting. The well camouflaged spiked larvae of Lonomia obliqua are often found clustered on tree trunks in Amazonia.

There have been thousands of cases where people have unwittingly touching or rubbed an arm against them. The effects can be extreme, including massive intercranial haemorrhaging and kidney failure. 

Lonomia larvae are a frequent cause of death in southern Brazil – 354 people died between 1989-2005. The fatality rate is about 1.7% – roughly equivalent to that of rattlesnake bites.

The Bullseye moth larva Automeris liberia ( Saturniidae ) can inflict a painful sting – Adrian Hoskins

unidentified Limacodidae species, West Malaysia © Gan Cheong Weei

Larva of Sphinx ligustri ( Sphingidae ), showing the spiracles and tail horn – Adrian Hoskins

Many people believe you can be stung by the ‘hornworm’ larvae of moths in the family Sphingidae but this is entirely untrue. The caterpillar is completely harmless, and edible to birds.

Mimicry

Diematic mimicry is quite a common form of defence in caterpillars as well as in adult butterflies and moths. The larvae of many Swallowtail species including Papilio polymnester and Papilio troilus have a pair of false eye-spots on the thoracic segments. Many hawkmoth larvae such as Deilephila elpenor and Hippotion celerio employ the same strategy.

When alarmed the larvae of these species puff up the thoracic segments causing the eye-spots to expand. This is considered to be a form of diematic defence in which the larvae are mimicking the heads of snakes.

Camouflage and disguise

Many species use camouflage to escape detection, and are thus often coloured green to match the leaves on which they rest. The Lasiocampidae species illustrated below is very well camouflaged at rest among lichens and mosses. Others are disguised as flowers, feathers, twigs or bird droppings.

unidentified Lasiocampidae larva, Peruvian Andes, 2800m © Adrian Hoskins

Heraclides thoas, disguised as a bird dropping. Rio Alto Madre de Dios, Peru – Adrian Hoskins

Gregarious behaviour and larval webs

Generally speaking larvae which feed as solitary individuals tend to be palatable to predators, and rely primarily on camouflage – colours, patterns and textures which help them to avoid detection. Larvae which feed gregariously tend to be unpalatable or toxic to predators. They often advertise their toxicity with bold aposematic colours – a seething mass of brightly coloured wriggling larvae is much more likely to deter a potential predator than a single larva could.

Gregarious behaviour also serves other purposes, e.g. a group of larva can quickly construct a communal silk shelter in which they can hide from predators and parasitoids. These larval shelters or nests also protect them from the ravages of extreme weather such as heavy rain, flooding and high winds.

Reflex bleeding

If molested, some species such as the caterpillar of the Peacock butterfly Inachis io react by ‘reflex bleeding’, i.e. they spurt a foul smelling and noxious fluid from glands behind the head. This acts as a warning to wasps, spiders and predatory birds that they are distasteful and should be left alone.

Molestation also causes the caterpillars to wriggle violently and drop from their leaf into the herbage below, presumably as a defence against parasitoid wasps or flies. Nevertheless at least 90% of Peacock larvae fall victim to attack by the Tachinid fly Zenilla vulgaris. Other Tachinids including Pelatachina tibialis, Sturmia bella and Phryxe vulgaris are also recorded as parasitizing Inachis io.

Inachis io, 5th instar larva, Hungerford, Berkshire – Adrian Hoskins

Multiple defence strategies

Birds rely primarily on sight to locate prey, so the evolution of visually directed defences such as camouflage, disguise and aposematic colouration reduces the likelihood of larvae being eaten.

These strategies work quite effectively against vertebrates but they provide no protection against invertebrates such as spiders, wasps, bugs and ants, which rely primarily on smell to locate their prey. The larvae of many species have consequently evolved a twin pronged defence strategy:The larva of the Puss moth Cerura vinula uses disguise as it’s first line of defence.

When at rest its disruptive pattern of green and dark purplish-brown gives it the appearance of a curled up leaf with darkened edges. This illusion is reinforced by the presence of a pair of tail prongs which are held together, simulating a leaf stalk.

The disguise helps it avoid being spotted by birds, but offers it no protection against parasitoid wasps that track victims down by scent. To deal with wasp attacks it switches to active defence mode. When molested it rears up and retracts its head. This causes the prothorax to expand, exposing a bright crimson ‘false head’, complete with prominent false eyes.

If this is insufficient to deter an attacking wasp the larva then spreads its tail prongs and everts a pair of whip-like threads which are waved angrily. Even this may not be enough to deter a wasp however so a last resort defence the larva can eject formic acid – the same chemical used by bees, wasps and ants in their stings.

Most Swallowtail larvae are palatable to birds and employ cryptic colours and patterns as their first line of defence. If discovered however they activate additional defences. Many for example have a pair of ‘false eye’ markings on the thoracic segments, and can inhale air through the spiracles to puff up the thorax, emphasising their threatening appearance.

This is often enough to deter birds from attacking. Molestation by insect predators and parasitoids however elicits a different response from the larvae. In this instance they evert the ‘osmaterium’ behind their heads. This discharges airborne isobutyric and 2-methylbutyric acids which has been shown to repel ants and Homopteran predators. It also deters oviposition by parasitoid wasps and flies.

Peruvian Cattleheart larva Parides anchises with osmaterium extended – Adrian Hoskins

Geometrid moth larvae use disguise as their primary defence – they look just like tiny twigs, and reinforce this similarity by stretching out their bodies in a straight line so that they project twig-like from a sprig of their foodplant.

If molested they release grip on the sprig, dropping instantly from a bungee-cord of silk. They dangle at the end of this thread until the attacker has moved on. After a while they haul themselves back up, consuming the silk thread as they do so.

Caterpillars of species such as the Small Tortoiseshell Aglais urticae, the Tiger moth Arctia caja and the Fox moth Macrothylacia rubi try to escape when they perceive a threat. If alarmed they simply roll into a ball and drop to the ground. 

Aglais larvae are covered in spines. Arctia and Macrothylacia larvae are hairy. In both cases birds remember from previous experiences that such larvae are difficult or uncomfortable to swallow, and sight-reject them.

A larva has only 2 functions during it’s life – to eat and survive. It’s basically just an eating machine with large powerful jaws, a huge gut, and a highly elastic skin that stretches to accommodate the huge amount of food consumed.

Larvae do not possess external wings. Even the tiniest larvae however have rudimentary wing-pads under their skin. These are initially extremely small, but by the time the larvae are fully grown the wing pads have developed veins and other structural features found in adult butterflies.

Head of 5th instar Polyura hebe ( Nymphalidae ), Singapore – Horace Tan

All butterfly larvae have six true legs located on the first 3 segments. These legs are used primarily for holding and manipulating the leaves on which they feed. On the abdominal segments they have 4 pairs of false legs called prolegs.

These “walking” legs operate by hydraulic pressure. Each has a rosette of microscopic hooks around its base, which enable the larvae to maintain a strong grip on twigs or leaves. There are also a pair of gripping anal claspers at the tail end of the body, which are used to secure the caterpillar while the prolegs are doing the walking.

The spiracles can be seen clearly on this Cerodirphia Saturniid larva from Peru – Adrian Hoskins

Caterpillars breathe through oval spiracles which open and close to allow gas exchange with the atmosphere. There are 2 spiracles per body segment, one on each side of the body.

Caterpillar of Privet Hawkmoth Sphinx ligustri ( Sphingidae ), England – Adrian Hoskins

Most butterfly eggs undergo colour changes as the young larvae develop within them. The eggs of the Marsh Fritillary Euphydryas aurinia for example are pale yellow when first laid, but after a day or two turn pinkish-brown, then deep crimson, and finally dark grey just before the larvae hatch. The eggs of the Orange tip Anthocharis cardamines are pure white when first laid, but turn orange within 2-3 days, then become dull grey when hatching is imminent.

Anthocharis cardamines – the egg on the right is freshly laid – Adrian Hoskins

When a caterpillar is ready to hatch, it bites a tiny hole out of the top of the egg, and over a period of an hour or so, nibbles away until the hole is large enough to allow it to crawl out. Some species use a different technique, nibbling a circle around the perimeter of the egg to create a “lid” which is pushed upwards to allow the caterpillar to make its exit.

After hatching, some caterpillars such as that of the White-letter Hairstreak Satyrium w-album rush immediately away and eat their way into a young leaf bud or flower. Most larvae, however, stay long enough to partly devour their eggshell, which contains vital nutrients. If deprived of the opportunity to eat the eggshell, caterpillars usually die.

Feeding

For the remainder of the larval stage, most species feed on the leaves, stems, flowers, or seeds of particular plants. Some species are polyphagous, i.e., they are adapted to feed on a wide variety of plants from different botanical families.

Most, however, are monophagous, i.e., limited to feeding on just one or two closely related plant species, and unable to survive on anything else. Many species in the family Lycaenidae are carnivorous, feeding on ant grubs or aphids. This group is dealt with in detail on the cannibals, carnivores, and myrmecophiles page.

1st instar Spilosoma luteum larva nibbling tiny holes in the lower cuticle of leaf – Adrian Hoskins

Larvae and adult butterflies of any given species generally use different sources of food. For example, Marsh Fritillary caterpillars eat the leaves of devil’s bit scabious, but the adult butterflies feed on the nectar of buttercups, milkworts, and thistles. In temperate areas, the larvae and adults live at different seasons, but in the tropics, the two stages often co-exist at the same time of year, so the dichotomy between larval and adult feeding behavior enables them to avoid competing for food.

The chemical makeup of plants changes seasonally. Plants often accumulate toxins in their leaves as a means of defense against caterpillars. Older leaves are more strongly toxic and have less protein than younger leaves. Towards the end of the season, leaves may be so toxic that they can kill any caterpillar that eats them. Therefore, the larval stage of many species, particularly oak feeders, tends to be compressed into the early part of the season.

Some species which breed on less nutritional plants need to spend several months in the larval stage, so towards the end of the season, they need to search out the freshest and least toxic leaves to survive. Some species even switch to alternative host plants that come into leaf later in the year. Caterpillars often feed on different parts of their food plant at different stages in their growth.

The balance of proteins, carbohydrates, minerals, alkaloids, and essential oils in plant leaves varies considerably at different times of day. Caterpillars therefore tend to feed at specific times when the foliage is most nutritional and least toxic. Some species feed at dawn, others in mid-afternoon, and others at night.

There are further reasons why many caterpillars only feed nocturnally. Firstly, they are less likely to be preyed upon by insectivorous birds, which need daylight to locate their prey. Secondly, larvae of Satyrinae and Hesperiinae, which feed on grasses—and species which feed on herbaceous plants—are prone to be accidentally consumed by diurnal grazing animals such as rabbits, sheep, or cattle. To avoid this, they evolved to become nocturnal feeders and, in the daytime, hide away deep down in grass tussocks where grazing animals can’t reach them.

The duration of the larval stage varies according to the nutritional value of the food. Species which eat foods with high nutritional value (flowers, fruits) grow quickly, going from egg to pupa in less than a month. Species which feed on leaves take up to 2 months. This is because leaves are harder to digest, and often contain toxins that need to be processed. Slower still are the species which feed on grasses, bamboos, palms, or roots, all of which are low in nutrients and particularly difficult to digest. In these species, the larval stage usually lasts at least 3 months.

In the case of species from temperate regions, growth is often so slow that the larvae are unable to complete their development during the summer and have to hibernate and resume feeding the following spring.

Moulting

Depending on the species, caterpillars increase their body weight between about 60-200x in the period between hatching and pupating. As it feeds and grows, a caterpillar’s elasticated skin periodically becomes too tight and has to be moulted and replaced with a looser, baggy, elastic second skin that forms under the outer skin. Moulting is triggered by nerve cells called scolopidia, which detect stretch in the skin between the caterpillar’s segments.

Two or three days before moulting, caterpillars anchor themselves either to a small button of silk which they have spun on a leaf or twig, or to a silk web spun over the foodplant.

A day or two prior to moulting, the soft tissues within the caterpillar’s head retract, forming a new head capsule which is temporarily housed within the first thoracic segment. When moulting takes place, the old head shell slides forward and drops off. The old skin then splits just behind the head, allowing the caterpillar to walk forward out of its former costume.

At first, the new skin is loose and soft, leaving the larva highly vulnerable to attack by parasitoid wasps and flies. The larva slowly inflates its body by drawing in air through the spiracles. After a couple of hours, the larva’s mandibles (jaws) have hardened, at which point a larva will often eat its old skin. Another 2 hours or so later, the skin has toughened sufficiently to allow the larva to walk about without injuring itself, and to resume normal feeding.

The stages between moults are known as instars. Caterpillars of the family Lycaenidae usually have 4 instars. Those of the Hesperiidae, Nymphalidae, Papilionidae, and Pieridae usually have 5 instars. The Riodinidae have between 6-8 larval instars according to species.

Leaf-miners

The newly hatched larvae of some moths, known as “leaf-miners,” burrow into leaves and spend their entire lives living and feeding between the upper and lower membranes. Each species leaves its own characteristic trail as it weaves its way about between the membranes. When the larva is fully grown, it emerges and pupates on the surface of the leaf.

Leaf-mines produced by caterpillars of the moth Stigmella aurella – Adrian Hoskins

Not all caterpillars feed on living flowers or leaves. Calycopis and Detritivora, for example, feed on dead vegetation on the forest floor, while some moths such as Cossus cossus live within tunnels in the trunks of dying trees, chewing their way through solid wood.

Larval webs and shelters

The caterpillars of many butterflies, including Peacock, Small Tortoiseshell, and Marsh Fritillary, live gregariously. They spend most of their lives within substantial silk webs. They emerge periodically to feed, but then retire to the silken shelter where they are protected from predators, parasitoids, and severe weather. These species tend to molt synchronously, after which they move as a group to another clump of foliage where they spin another web.

The communal web of the Small Eggar caterpillar ( Lasiocampidae ) – Adrian Hoskins

Many other species live solitarily and construct individual shelters or tents in which they hide while resting. These include skipper butterflies (Hesperiidae), Pyralid moths (Pyralidae), and Charaxine butterflies in the genera Memphis and Consul. The latter hide in rolled leaves and plug the entrance with their head capsule. This is sclerotized and too hard to be pierced by the ovipositor of parasitoid wasps. Other parasitoids such as Tachinid flies cannot gain access to lay eggs on the larva’s body, and the secrecy provided by hiding in the shelter also undoubtedly confers a degree of protection from birds and other foraging predators.

Case-bearing larva of bagworm moth Psyche casta ( Psychidae ) Berkshire, UK – Adrian Hoskins

Bagworms

Some of the most primitive and interesting larvae are those of the case-bearers (Coleophoridae) and bagworm moths (Psychidae). These species provide part of the evidence that links butterflies and moths (Lepidoptera) to the insects from which they evolved, i.e., caddisflies (Trichoptera).

In common with caddis larvae, the caterpillars of Coleophoridae and Psychidae construct shelters or bags made from silk and natural materials such as dead leaves, bits of wood, lichens, or grains of sand. The cases have a tubular exit hole at the front end, and a small hole at the rear from where excrement is ejected. The larvae never leave their cases, so as they grow, they have to continually add more material to the front of the case to accommodate their increasing size.

When moving from place to place, the larvae anchor themselves to the inside of the case with their anal claspers and extend the front of their bodies out of the case, just far enough to allow them to grab hold of the substrate with their three pairs of true legs to haul themselves along.

The larvae within the cases are all very plain creatures, so it is usually easier to identify a bagworm or case-bearer from the design of the case, which is different for every species. The cases measure from about 1cm in the smaller temperate species, up to 15cms in some tropical species.

When the caterpillar is fully grown, it secures the case to a twig or branch, and pupation takes place within the case. Male moths are winged, but females of most species are wingless and usually don’t possess antennae, eyes, or legs. Females never leave their larval case. When copulating, the male reaches into the case with his abdomen to make sexual contact. The female lays her eggs inside the case and then dies.

The female of one species, the Evergreen bagworm Thyridopteryx ephemeraeformis, dies without laying eggs. Its tiny caterpillars emerge direct from the female body inside the case. Some species are parthenogenetic, i.e., their eggs develop without male fertilization.

Larva of unidentified bagworm moth, Bobiri, Ghana – Adrian Hoskins

Sexual Development

As larvae grow and mature, they begin to develop sexual organs internally, but it is not possible to determine the sex of a larva from its external appearance. However, there are some species of Lepidoptera in which the larvae that will ultimately become males have 4 instars, while those that will become females have 5 instars.

An example is the Vapourer moth Orgyia antiqua, in which the female larvae grow to a much larger size than the males. The male moth looks much like any other moth, but the female is wingless and has an enormous abdomen swollen with hundreds of eggs.

Duration

In tropical regions, larvae can develop very rapidly, and in some species, the entire larval period may be as short as 2 weeks. In temperate regions, the larval stage usually lasts about 6 weeks, but is often much longer. Many species, particularly amongst the Satyrinae, overwinter as larvae, taking several months to mature. There are even a few sub-Arctic species in which the larval stage can last for 2 years.

Larvae often find themselves on plants with insufficient foliage to sustain them, so at these times they naturally tend to wander in search of other plants. Often it can take a considerable time for a larva to locate another specimen of it’s foodplant, and starvation sets in.

It is normal for a starved larva to nibble intensely at any object it encounters. If the object happens to be another larva it is likely that its skin would be punctured, and the mouthparts of the attacker would come into contact with its body fluids. The fluids have a similar chemical content and taste to the foodplants of the larva, and hence cannibalism arose.

Cannibalism has two possible advantages for larvae – firstly by eradicating competitors they ensure they have enough leaves for themselves. Secondly, captive rearing has shown that cannibalistic larvae grow faster than non-cannibals, probably because they save themselves the time-consuming business of digesting and processing the vegetation.

The larvae of many species including the Orange tip Anthocharis cardamines and the Dun-bar moth Cosmia trapezina are cannibalistic. They normally feed on foliage but will attack and eat any other caterpillar that they encounter. Most members of the Lycaenidae also have very strong cannibalistic tendencies, and many are carnivorous on aphids or ant grubs.

Carnivores

The larva of the Large Blue Maculinea arion feeds in its early instars on the flowers and leaves of Thymus pulegioides, but is aggressively cannibalistic towards other larvae. Upon reaching the 4th instar it loses all interest in feeding, releases it’s grip on the foodplant and falls to the ground. It wanders about until it is located by a Myrmica sabuleti ant. The ant uses it’s antennae to caress the larva, stimulating it to secrete a honey-like fluid from the Newcomer’s gland on it’s back. After a while the larva taps its posterior segments against the ground, sending a vibratory signal to the ant. The ant then wanders off but returns later with other ants to further “milk” the larva.

After several milking sessions the larva becomes immobile and hunches it’s back. This allows the ant to seize it and carry it into the brood chamber of the ant nest. Once settled in its new home the larva becomes carnivorous, feeding on tiny ant grubs. Only the largest ant nests produce the 1500 or so grubs that are necessary for the Large Blue larva to complete its growth.

The larva is tolerated and protected by the adult ants in exchange for providing them with a regular supply of “honey” from it’s dorsal gland. It also emits pheromones and produces sounds that have been shown to appease the ants and assure its safety. The arion larvae spend several weeks in the ant nest, feeding exclusively on ant grubs until they pupate.

In Africa the larvae of Lepidochrysops have a similar association with Camponotus ants. Another Lycaenid species Euliphyra hewitsoni lives in the nests of Oecophylla tailor-ants, also feeding on a diet of ant grubs. Its cousin the Woolly Leg butterfly Lachnocnema lays its eggs amidst colonies of psyllid or membracid bugs. The resulting larvae feed carnivorously throughout their lives, attacking and devouring the tiny insects.

In Borneo, Allotinus apries feeds on coccids when it is small. As it grows bigger the larva develops protrusions on its body. These protrusions are used as grapples by an ant called Myrmecaria lutea which carries the larva to it’s nest. Thereafter the larva lives within the nest, feeding on ant grubs.

The extraordinary caterpillar of Liphyra brassolis lives inside the nests of weaver ants Oecophylla smaragdina, devouring hundreds of ant grubs. A single nest can house as many as 5 or 6 Liphyra larvae. Any other larva that found it’s way into an ant nest would be killed, but the tortoise-like Liphyra larva has a built-in survival kit in the form of a tough chitinous carapace that is impervious to ant bites. The ants repeatedly attempt to flip it over to reach the soft under-belly, but the larva uses it’s powerful sucker-like feet to pull the carapace down and seal it limpet-fashion against the substrate, defeating all attempts by the ants to gain entry.

Periodically the larva lifts the carapace slightly and pops it’s head out to snatch an ant grub with its mandibles. In an instant the grub is pulled under the carapace. The larva then pierces the skin of the grub, and sucks out the juices. The grub’s empty skin is then ejected, and the killer larva moves on to find its next victim.

The pupa of Liphyra brassolis is formed within the ant nest. The ants don’t attack the pupa as it is able to mollify them by using chemical deterrents, and by stridulating. Research on Lycaenids has demonstrated that the larvae and pupae of at least 150 species worldwide are able to generate a “melody” of audible chirps that appease ants.

Liphyra brassolis larva, Siem Reap, Cambodia – Dani Jump

By associating with ants, Lycaenid larvae gain protection from other small predatory insects which avoid ants in case they are attacked. For the same reason larvae are less likely to be attacked by parasitoids – one study found for example that ant-attended larvae of Glaucopsyche suffer much lower levels of parasitism by Braconid wasps and Tachinid flies compared with unattended larvae.

All documented Lycaenid larvae have one or more adaptations specialised for association with ants. They include the dorsal Newcomers organ which lies between the 7th/8th abdominal segments; and a pair of eversible tentacles either side of it. These secrete a substance similar to aphid honeydew, which acts as an ant-attractant. The substance contains glucose, sucrose, fructose and amino acids including serine, histidine, glutamic acid, lysine and arganine. The variable proportions of the amino acids gives the secretion of each species a distinctive “signature” which ensures that it attracts the correct species of ant.

Another adaptation of Lycaenid larvae is the presence of epidermal glands ( pore cupolas ) which exude substances that appease the normally aggressive ants. In combination these adaptations allow the larvae to manipulate the behaviour of ants for their own benefit.

Species that have dependent, mutually beneficial or symbiotic relationships with ants are known as myrmecophiles. The act of feeding on ants is called myrmecophagy. The act of feeding on aphids or other homopteran bugs is called aphytophagy.

The Evolution of Myrmecophagy and Aphytophagy

Myrmecophagy and aphytophagy probably have their origins in long-term exposure to ant-attended homopterans. The following hypothetical example might illustrate how such behaviours evolved:The larva of the Purple Hairstreak Quercusia quercus feeds on oak leaves. Ants forage on oaks to obtain honeydew, which they milk from aphids and from Quercusia larvae.

It is feasible that ants might at some stage in the future acquire the habit of carrying submissive quercusia larvae to their nests. There the larva might feed on substances regurgitated by ants, which are chemically similar to the oak sap that aphids convert into honeydew. Ants feed their grubs on these regurgitations, so the flesh of the grubs probably has a taste similar to oak leaves. A hungry Quercusia larva, which like most other Lycaenidae has cannibalistic tendencies, would soon start nibbling at objects in the ant nest, and it would not be long before it started to eat ant grubs.

In order for larvae to be able to co-exist with ants they had to evolve ways to protect themselves from attack. Lycaenid larvae for example have skin that is about 5 times thicker than that of those in other families of Lepidoptera, and is thus more resistant to ant bites. Another adaptation is the evolution of tough fleshy lappets along the lower edge of the caterpillar’s abdomen. These enable it to seal its body against the substrate, making it harder for an ant to flip it over to reach the soft underbelly. Ants have acute eyesight and tend to run towards moving objects, so Lycaenid larvae make themselves less obvious by adopting a slow gliding form of locomotion.

Lycaenid larval feeding

The table below lists the larval feeding behaviour of several genera of Lycaenidae. The subfamilies Lipteninae, Poritiinae and Lycaeninae have larvae which exclusively on plants. Larvae of Curetinae are plant-feeders and are attended by ants although there is no evidence yet of ants milking them. The Riodinidae, which some workers consider to be a subfamily of Lycaenidae, includes many species that are suspected of being carnivorous or aphytophagous.

More odd feeding habits

The moth Ceratophaga vicinella lays it’s eggs on the empty shells of dead Florida Gopher Tortoises Gopherus polyphemus. The resulting larvae feed gregariously on the keratin shells, constructing a mass of silk tubes which act as anchors, connecting the outer shell to the sandy substrate. Many moths have larvae that feed on dung.

These include Acrolophus pholetus and Idia gopheri, which both spend their lives feeding on dung within the burrows of the Florida Gopher Tortoise.

In Africa, the caterpillars of other Ceratophaga species feed in tunnels within the hooves and horns of antelopes and cattle. Ceratophaga species are members of the Tineidae – the family to which clothes moths belong. The larvae of the Case-bearing Clothes moth Tinea pellionella are notorious for their habit of eating holes in woollen fabrics but in the wild state live within bird’s nests, feeding on the keratin in hairs and feathers.

The larvae of the related Tapestry moth Trichophaga tapetzella feed on coarser fibres, and are also common in owl pellets ( regurgitated fur and bone ).

There is a constant battle between plants and the caterpillars which eat them, each evolving ways to try and stay ahead in the struggle for survival.

Plants have evolved a variety of methods to protect themselves from being eaten. Many extract minerals from the soil, and chemically convert them into toxic compounds – alleochemics, which in theory will kill caterpillars, or at least discourage them from feeding.

In practice however many caterpillars have evolved ways to avoid being poisoned. One method they use is to bite through leaf veins, stems or petioles to allow the toxic juices to bleed out before eating a leaf. Melinaea glasswing caterpillars for example cut circular trenches in leaves to cut off the flow of toxins, and then devour the enclosed tissue. Brahmaea caterpillars bite through stems to cut off the toxins and then feed on the drooping leaves. Other species simply restrict themselves to nibbling at the edges of leaves where toxicity is minimal.

Some larvae, e.g. Danaines and Ithomiines, have developed an immunity to the poisons, but store them in their bodies, or convert them into even more toxic substances which deter predators. The hawkmoth Isognathus leachi is toxic, and uses bold stripes to “advertise” its noxious properties to potential predators:

the larva of the Hawkmoth Isognathus leachi from Peru is poisonous to birds – Adrian Hoskins

In many cases the toxins sequestered from larval foodplants are passed forward to other stages of the lifecycle, e.g. in Ithomiines the toxic qualities are passed to the adult butterflies.

An interesting case is the neotropical Arctiid moth Utetheisa ornatrix, whose caterpillars feed on Crotalaria. From these plants they sequester pyrrolizidine alkaloids, a group of toxins that render the caterpillars unpalatable to birds. These PAs are stored within the bodies of the caterpillar, pupa and resulting adult moth, all of which inherit the toxicity and are thus protected from predators. They are also passed to the eggs, providing them with protection against a variety of predators such as ants, and from egg parasitoids.

Plants fight back !

When caterpillars develop an immunity to the toxins, the plants become threatened, and have to evolve other ways to protect themselves. Some grow thorns to make it difficult for caterpillars to walk on their leaves and stems, or develop tough leathery leaves that are difficult to digest.

Caterpillars of Parides Cattle Heart butterflies feed on Aristolochia vines, but some vines have found ways to defend themselves. They do this by only “permitting” the butterflies to lay a limited number of eggs. If “too many” eggs are laid, the leaf around each extra egg dies, and the dead tissue drops to the ground, carrying the egg with it !

In South America, Passiflora vines have evolved a seemingly “intelligent” means of protecting themselves from being eaten by the offspring of Heliconius butterflies. The butterflies normally only lay a single egg on each Passiflora, so as to minimise competition between siblings for food.

Some Passiflora species have “learned” to make use of this fact by randomly producing tiny structures on their leaves or stems which mimic Heliconius eggs. Whenever a Heliconius detects an egg – or a false egg – it is inhibited from laying “further” eggs on the plant, so the vine effectively prevents butterflies from ovipositing on it.

Another vine Passiflora adenopoda has evolved a different trick – its leaves and stems are covered with a coating of sharp microscopic hairs which puncture the skin of browsing caterpillars, rendering them immobile, and killing them by starvation.

When a larva becomes full grown, it undertakes a final moult to become a pupa. For a day or two prior to pupation the larva goes through a wandering phase when it usually leaves its foodplant and may walk up to a kilometre before finding a suitable place to undertake the transformation into a pupa. During this phase it is very prone to predation. Dispersal however probably reduces overall predation of pupae by spreading them over a wider area – if they were concentrated on or around the foodplant it would be easier for birds to home in on them and wipe out the whole brood.

Larvae pupate in different ways depending on which family they belong to. A larva from the family Nymphalidae for example will spin a tiny button of silk on a leaf or stem, and anchor itself to it by its tail. The tail has an appendage called a cremaster, which is equipped with microscopic hooks to hold it securely to the silk.

Larvae of Papilionidae and Pieridae do the same, but additionally spin a silken girdle around their waist. Lycaenidae and Riodinidae don’t possess cremasters so they either pupate on the ground, or attach themselves by a silk girdle to a leaf or stem. Hesperiidae pupate loosely, usually within a flimsy silken tent. The larvae of most moths pupate loosely in a chamber just below the surface of the ground. Others, including Saturniidae, Bombycidae and Lasiocampidae pupate inside a tough silk cocoon spun on the leaves, stems or branches of their foodplants.

The pre-pupal caterpillar remains motionless for 2-3 days preparing itself for its final moult. During this time the prolegs start to shrink, the thoracic segments become enlarged, and the larva adopts a curled hump-backed position.

Gonepteryx rhamni, fully grown larva ( pre-pupa ) just prior to the final moult – Adrian Hoskins

When the final moult takes place the skin splits behind the head, but instead of a caterpillar walking out of the old skin, what emerges is quite different in nature – a legless, wriggling, non-eating entity called a pupa or chrysalis.

At first the pupa is soft, limp and highly vulnerable to attack by parasitoid wasps and flies. Within a few hours however the skin hardens into a tough shell that will protect the insect until it ultimately emerges as an adult butterfly or moth.

The pupae of many Lycaenidae species are attended by ants ( see myrmecophily ). The presence of ants is beneficial to the pupae because ants drive away predatory insects and parasitoid wasps that would otherwise attack them. Experiments with the Australian hairstreak Jalmenus evagoras for example have shown that in cases where ants have been denied access to the pupae the latter have suffered up to 95% parasitism by the wasp Brachymeria reginia. Conversely, pupae attended by the ants experienced zero parasitism.

Siproeta epaphus ( Nymphalinae ), Peru – Adrian Hoskins

Caterpillars show no external evidence of sexuality, but pupae can be distinguished as male or female. A male pupa will have 2 tiny bumps close to it’s tail, corresponding with the anal claspers of the adult butterfly or moth. It is also usually slimmer and lighter than a female pupa.

Many other anatomical details of the adult butterfly can be seen on the pupa – e.g. antennae, legs, eyes, wing cases and palpi.

Anthocharis cardamines ( Pierinae ), pupa attached to garlic mustard stem – Adrian Hoskins

Butterflies in the families Nymphalidae, Papilionidae and Pieridae usually pupate openly, attached to leaves, stems or twigs. These unprotected pupae are highly vulnerable to predation and parasitism. They are usually cryptically coloured and patterned to resemble foliage, lichens, bird droppings or other common natural objects. This protective resemblance makes it much harder for birds and small mammals to locate them, and increases their chances of survival.

Many species of Papilionidae and Pieridae are able to increase their chances of survival individually, by producing pupae which differ in colour according to their surroundings. Laboratory experiments have shown that on the days prior to pupation caterpillars can detect the colour of the surrounding vegetation and that this triggers a genetic response which decides whether the ultimate pupa will be green or brown.

Speckled Wood Pararge aegeria ( Satyrinae ), pupa attached to pendulous sedge – Adrian Hoskins

Many butterfly pupae in addition are adorned with spines, keels, knobs and other protrusions. They are also frequently contorted into strange shapes. The overall effect is that they often very strongly resemble twisted and desiccated dead leaves or bits of wood. Other butterflies such as Ithomiinae and Danainae are smooth, bulbous and silvery, looking like glistening rain drops.

Heliconius pupa, probably melpomene ( Heliconiinae ), Rio Madre de Dios, Peru – Adrian Hoskins

The use of protective resemblance as described above is a form of passive defence, but there are a small number of pupae which use active defence e.g. the neotropical Brassoline Dynastor darius has a pupa that resembles a snake’s head. Another well known example is the pupa of the Deaths Head Hawkmoth Acherontia atropos, which wiggles and squeaks if molested. The squeaking sound is produced by forcing air in and out of the spiracles.

Cocoons

Most Skipper larvae ( Hesperiidae ), and those of moth families including Lasiocampidae, Arctiidae, Saturniidae, Notodontidae and Zygaenidae pupate within cocoons. These range from flimsy affairs composed of little more than a few strands of silk, to hardened shells made of dozens of layers of silk interwoven with bits of chewed bark, such as that of the Puss moth Cerura vinula.

Some cocoons are formed among living foliage on trees and bushes, while others including that of the American Moon moth Actias luna are formed among dead leaves on the forest floor. The cocoon of the Emperor moth Saturnia pavonia has a lobster-pot design with a special “door” which allows the moth to make its escape, but prevents other creatures from entering.

One of the strangest and most beautiful cocoons is that of the Amazonian moth Urodus ( Urodidae ) which has a coarse open mesh design with an exit at the bottom, and hangs like a pendulum from a 20cm long silk cord. It seems likely that the cord may function to isolate the pupa from marauding ants, but little is known about the biology of this species.

Urodus cocoon, Peru – Phil Torres

The cocoons of the silkworm moth Bombyx mori ( Bombycidae ) have been used for centuries for the production of silk. Several species in the family Saturniidae including Antheraea mylitta also produce silk of commercial quality.

Diapause

The pupal stage of the lifecycle can last anything from 1 to 40 weeks depending on the species. In polyvoltine species ( those which have more than one generation per year ), the summer pupal stage will be short – often just a few days; but the 2nd brood may overwinter as a pupa from August or September until the following May or June. 

Some species occasionally delay their emergence and remain as pupae for 2 or more winters. This is a natural safeguard because in an unusually short or harsh summer a species might be unable to breed in viable numbers. By staggering its emergence over 2 or 3 years it spreads the risk and ensures that at least a few adults will appear and reproduce each year, regardless of the weather.

Metamorphosis

The popular belief that the bodily fluids within the pupa break down into a “soup” and later reform in the shape of a butterfly is largely untrue. The change from larva to adult butterfly is actually a very gradual process. Clusters of stem cells from which the wings develop are present in segments 2 and 3 of small larvae.

They replicate and diversify during larval development. In the last few days prior to pupation the development accelerates, so that the wings are almost fully formed at the time of pupation. The same applies to the antennae, eyes and palpi, all of which are visible on the newly formed pupa. 

Within the pupa the changes that take place are surprisingly minor. The wing scales develop as plate-like extensions from cells on the wing surface. The heart, brain, eyes, antennae, proboscis etc all develop from the fairly simple organs “hidden” within the larva, into the recognisable features of an adult butterfly.

Gonepteryx rhamni with wing patterns showing through, just prior to emergence – Adrian Hoskins

About 2 or 3 days before the butterfly is due to emerge it changes colour, and the colour and pattern of the wings can usually be clearly seen.

At this stage female pupae of many species exude pheromones which attract males even before the butterfly has emerged. In Costa Rica e.g. I have observed that female pupae of Heliconius erato, when close to emergence, often have several male adults in very close attendance.

A frantic battle takes place the instant the female hatches, as all the males struggle to copulate with her, not even allowing her time to expand and dry her wings. The mated pair then have to endure the continuing aggravation of the remaining males, which are often extremely persistent, trying to prise the pair apart. Eventually, with the approach of dusk, the unsuccessful males disperse, allowing the pair to remain copulated until the next morning.

Emergence of the adult butterfly or moth from the pupa is triggered by factors including humidity, temperature, light level and time of day. Most butterflies emerge shortly after dawn.

The spiracles of the butterfly within the pupa are linked by short tubes to the spiracle openings on the pupa shell. Just prior to emergence air is drawn in through these tubes, enabling the butterfly to pump up its body, which causes the shell of the pupa to split, just behind the head.

The butterfly then forces its way out, using its legs to pull itself clear of the empty pupal shell. If the pupa was formed within a silken shelter, as is the case with most Hesperiidae species, the butterfly first ejects solvents from the proboscis. These soften the silk enough to allow it to push its way out.

Eueides lybia, newly emerged from chrysalis, Rio Madre de Dios, Peru – Adrian Hoskins

Having emerged and settled into position, the insect then spends several minutes hanging virtually motionless. During this time it pumps fluids into the wing veins, causing the wings to expand to their full size. After drying the wings, and before taking their first flight, butterflies and moths expel the metabolic waste product meconium from their abdomens, in the form of a pinkish liquid. Male butterflies usually fly off as soon as their wings are hardened, but females of many species tend to stay within a few metres of the emergence site until mated.

Sex ratios

It is often claimed that more male butterflies emerge than females. The most quoted example is of Rajah Brooke’s Birdwing Trogonoptera brookiana whose males are sometimes stated to outnumber females by a ratio of as much as 10:1. These claims however are caused by sampling inadequacies – females of most species are more secretive in behaviour, better camouflaged, and tend to spend most of their lives in habitats that are less accessible to observers, e.g. in the forest canopy.

Males on the other hand tend to be more colourful and are considerably more visible in their behaviour, e.g. males of brookiana and many other species habitually aggregate in large numbers to imbibe moisture from muddy ground. Captive breeding experiments with brookiana and hundreds of other species have proven that both sexes actually emerge in similar numbers.

In most species males emerge at least a day or two before females. The explanation usually given for this is that females usually mate on the day they emerge, so it is advantageous if there are already plenty of males available to them. Another factor not usually mentioned in literature is that males of some species are not capable of mating until they are 2-3 days old.

This is because they need to feed in order to accumulate alkaloids that are vital to reproduction. Well known examples of this include the Purple Emperor whose males feed at dung, Swordtails and Daggerwings which feed at urine, and Glasswings such as Pteronymia sao which feed on decomposing plant material. The latter derive pyrrolizidine alkaloids from the plants, which are used in the production of pheromones and defensive toxins, as well as for reproductive purposes.

Feeding behaviour

Males of many tropical species are regularly observed imbibing dissolved minerals from damp mud, bird droppings, aphid secretions, sap runs, or even from carrion. The minerals are later passed to the females during copulation, and may contain vital nutrients necessary for the production of fertile eggs.

In temperate regions both sexes of most species feed primarily at nectar, but males of several species, e.g. Apatura iris, Lysandra coridon, Pyrgus alveus, Thymelicus lineola and Mellicta athalia commonly imbibe mineralised moisture, or visit dung.

Certain members of the subfamily Heliconiinae are unusual in that their females use nectar to dissolve pollen which they collect from rainforest flowers. Studies by Gilbert of captive Heliconius ethilla in Trinidad have shown that females deprived of pollen only lay about 15% of the number of eggs laid by females that have access to pollen.

The pollen provides nutrients that cannot be sequestered from other sources, and contributes greatly to the longevity of the butterflies. They have been recorded as living for up to 8 months as adults – most other tropical species live for only a few days.

Heliconius xanthocles, sequestering pollen from Psychotia ‘hotlips’ flowers – Adrian Hoskins

Butterflies tend to have short lives. Females of most species often have less than a week to find a mate, copulate, search for oviposition sites, and lay their eggs. Rapid mate location and recognition are therefore vital – butterflies can’t afford to waste time on fruitless encounters with species other than their own.

Orange tip Anthocharis cardamines, male, Dunsfold, Surrey, England – Adrian Hoskins

Butterflies can see all the colours of the visible spectrum, plus ultra violet. Brightly coloured species such as the Orange tip Anthocharis cardamines are able to detect others of their own kind from several meters away. Experiments with bright blue Morpho species show that waving blue foil in the air is very effective at attracting them towards observers.

Several researchers have attempted to unravel the mysteries of visual communication / recognition in butterflies. Magnus found that males of Argynnis paphia used “paper butterflies” attached to a rotor arm to test the reaction of male Argynnis paphia to numerous variations of colours, shapes, sizes and patterns in paper females. A normal paphia female is dull orange in colour, spotted with black, and has a gentle fluttering flight.

Magnus found however that the “ideal” female, i.e. the paper variant most attractive to the male, was plain orange, up to 4 times the size of the male, and had a very rapid wing flutter-frequency of about 120 Hz. This poses the question – why didn’t female paphia evolve to have huge bright orange wings ?The answer is probably that the normal spotted female has sufficient orange content to attract the male, while a plain orange female would be too conspicuous to predatory birds.

A spotted pattern is an effective camouflage, given that the female spends the most important part of her life i.e. the oviposition stage, fluttering around in the dappled sunlight of mature woodlands. A plain orange female would attract males more easily, but would quickly be found by birds, and would not live long enough to lay her eggs.

Papilio machaon – a species with an instantly recognisable pattern – Adrian Hoskins

While wing colour is important in the initial stages of mate location, pattern recognition is a different matter, and only comes into play when the butterflies are in close proximity. Conspicuous patterns such as the black and yellow pattern of Papilio machaon, or the black, red and white of Vanessa atalanta may be recognised at close distances, but it is obvious that subtle patterns cannot be.

To illustrate this point, simply imagine an alpine meadow with a mixed population of Erebia species. All are very drab brown insects of similar size and shape, differing only in minute details that could not possible be seen with the poor resolution of a butterfly’s eyes. The same argument applies to the Pyrgus skippers, the Melitaea Fritillaries and the numerous Polyommatine blues, where many very similarly patterned and closely related species share the same habitat.

If butterflies relied solely on visual stimuli for mate recognition they would waste almost all of their short lives chasing after the wrong species, and reproduction success would be very low indeed.

Mate recognition

During the initial “approach” phase of mate location males will chase after almost any small moving object including falling leaves, bees, and butterflies of any species and either sex. After this initial contact, follow up behaviour depends on the response of the chased object. Birds are avoided but other butterflies are always investigated, using a combination of visual and chemical cues.

Ultra-violet patterns on the wings often enable butterflies to recognise their own species. When butterflies get close to each other they use chemical messaging, in the form of pheromones, which provides additional confirmation of species, and tells them whether they are of the same or opposite sex.

If the pheromones indicate that the object being pursued is a conspecific male, the butterflies are often stimulated into aerial dogfights in which they battle for ownership of good vantage points from which to intercept passing females. These territorial battles can last for several minutes, after which one male is ousted from the vicinity.

Alternatively, if the pheromones indicate that the object being pursued is a conspecific female, the male is stimulated into initiating courtship. In many species exposing a female to male pheromones is enough to initiate instant copulation, but in other species a complex courtship ritual involving a protracted series of visual, tactile or olfactory stimuli and responses is necessary before copulation can take place.

Flowchart : behavioural cycle of a typical butterfly 

Pupal mating

In the genus Heliconius most species rely entirely on airborne chemicals to locate mates. Males of hecale, ismenius and cydno are attracted by pheromones to the pupae of conspecific females. The day before emergence a female pupa will usually have several males in close attendance. A frantic battle takes place the instant she hatches, as the males all struggle to copulate with her, not even allowing her time to expand and dry her wings.

In some other Heliconius species such as hecalesia, hewitsoni, erato, charithonia and sara the males don’t even wait until the female emerges. Instead they physically break open her pupa and copulate as soon as her genitalia are accessible.

Androconia

Males of Satyrinae, Hesperiinae, Pyrginae and Theclinae have specialised scales on their forewings called androconia. These have sacs at their bases containing pheromones which they disseminate into the atmosphere via tiny hairs or plumes on the edges of the scales. The pheromones are used to attract females and entice them to copulate.

In Danainae the androconia are on the hindwings. The males have tufts of hair-pencils at the tips of their abdomens which they brush against the androconial scales to collect pheromones. These are later disseminated by expanding the tufts when in the presence of females.

Males of several Ithomiine species gather at “leks”, where they release pheromones from hair-like androconial scales on the upperside hindwings. These attract more males, which release further pheromones. After a few days a lek may include a dozen or more different Ithomiine species. Passing females are attracted by the complex fragrances, and their presence stimulates the males to open their wings and release further pheromones that entice the females into copulation.

Courtship rituals

The courtship behaviour of butterflies in general is inadequately studied, but it is clear that in most species the female will not permit the male to copulate until he has completed an often complex ritual. This typically begins with the male releasing airborne pheromones, which leads to the female settling on foliage. The male might then begin a “courtship dance” around the female, whirring his wings to waft his pheromones across her antennae.

If the female accepts his advances ( she may instead give him a rejection signal ), there is often a confirmation ritual in which contact pheromones ( cuticular hydrocarbons ) come into play. A well known example is the Grayling Hipparchia semele, in which the male clasps the females antennae between his wings to bring them into direct contact with his androconial scales. The Orange Sulfur Colias eurytheme behaves in exactly the same way.

Another example is the Wood White Leptidea sinapis, in which the male and female sit on a leaf, facing each other, exchanging chemical messages with their antennae. The male repeatedly flicks out his long proboscis, whipping the female alternately on the underside of her left and right wings. Both sexes periodically flick open their wings. The butterflies are clearly communicating something but the ritual does not appear to instigate copulation, so the nature of the “messages” is unclear.

Wood Whites Leptidea sinapis engaged in courtship ritual – Adrian Hoskins

Small Tortoiseshells Aglais urticae have a protracted courtship which can last for several hours. The male follows the female as she flies from place to place. When she settles and opens her wings, he walks onto her hindwings, tapping them with his antennae. The process is repeated numerous times over several hours, during which the male will drive off any other intruding males. Eventually the female leads him to a sheltered spot, typically beneath a small bush, where copulation takes place.

Brimstone Gonepteryx rhamni males are also commonly seen “wing-walking” on females, but this is invariably followed by the female inverting her wings and raising her abdomen – a signal to the male that she is rejecting his advances, and a sign that she has already mated ( females of most butterflies only mate once ).

Brimstone Gonepteryx rhamni, female raises abdomen to signal rejection to male – Adrian Hoskins

When female Brimstones are receptive, copulation takes place almost instantly, without any observable pre-nuptial ritual. Most butterflies remain copulated only for an hour or so, but the Brimstone is quite remarkable in this respect – I once found a pair of Brimstones which remained copulated beneath a bramble leaf for an amazing 17 days before finally parting company !Males usually mate with several females in the course of their lives.

Females of certain long-lived species such as the Monarch Danaus plexippus will mate with several males, but in the majority of species females normally only mate once. After mating, the genital opening on the females of Marsh Fritillaries Euphydryas aurinia and some other species becomes sealed, physically preventing them from mating with other males. Males of the Apollo butterfly Parnassius apollo seal the female genital opening with a structure called a sphragis to prevent other males from copulating.

In the case of species which hibernate as adults, copulation occurs in the spring. Brimstones for example emerge in July, feed for a few weeks, and then go into hibernation for several months. After awakening the following April, they are mated, and then the females fly many miles, often across inhospitable terrain, stopping to lay their eggs on any buckthorn plants that they encounter on their travels. The butterflies thus spread throughout the countryside, interbreeding with other Brimstones that may have originated a considerable distance away.

The resulting high genetic diversity is probably a major factor in the remarkable success of the species, which is able to exploit an enormous range of habitats and climatic extremes, being found at altitudes from sea level to 2800m, and having a range that encompasses north Africa, the whole of Europe, and extends across temperate Asia to Siberia and Mongolia.

Perching, patrolling, and territories

Entomologists have traditionally divided the pre-nuptial behaviour of butterflies into two groups – those that “patrol” and those that “perch”.

Patrolling species are those where the male actively patrols a regular or random route through it’s habitat in order to locate a female. Perching species are those where the male spends long periods sitting on a prominent projecting leaf, or on a particular rock or patch of ground, which it uses as a vantage point from which to intercept passing females. These vantage points form the bases of territories, which the males will vigorously defend against other intruding males.

If two males meet, they twist and turn around each other in the air, and end up spiralling upwards to a great height until the “intruding” male ( usually a newly emerged individual which has not yet found it’s own perch ) is ousted from the territory.

A perch is simply a vantage point from which males can get a good view of all passing insects. Each species has it’s own preferred type of perch however – the Purple Emperor Apatura iris will perch at the top of a prominent tree, usually on a hilltop, while the Duke of Burgundy Hamearis lucina will perch on the leaf of a bush, typically in a small glade or at the sunny intersection of forest paths. In both cases the butterflies have homed in on a spot where they have a good view in all directions, and can survey and intercept passing females.

In practice, any male, of either a patrolling or perching species, will intercept any other flying insect of similar size and colour, to investigate it and determine whether it is a female of it’s own species. Most males will try to fly over or around a female in a particular direction. A Silver-washed Fritillary male for example will loop over and under a female as she flies along a track, showering her with pheromones. A Silver-spotted Skipper male on the other hand will perform a figure of eight dance around a settled female, whirring his wings to waft pheromones over her antennae.

Lysandra bellargus copulating pair ( female on left ) – Adrian Hoskins

Lekking

In South American rainforests and cloudforests male Glasswings and Tigers ( Ithomiinae ) often gather at ephemeral “leks”. It usually takes about 3-7 days for a lek to form, and it may exist for up to 3 months, during which time numerous individual males will come and go.

At the leks males release pheromones from hair-like androconial scales on the uppersides of their hindwings. These pheromones attract more males, which release further pheromones. After a few days the lek may contain between a dozen and several hundred individuals, comprised of up to 20 or 30 different Ithomiine species.

Passing females are attracted to the leks by the complex fragrances. Their presence stimulates the males to open their wings and release other pheromones that entice the females into copulation.

Male and female butterflies of any given species usually behave very differently. In most species the males are highly active, and their behaviour follows a predictable cycle of feeding, basking, and patrolling in search of females. Males of other species are often highly territorial, and will defend their territories against other insects including wasps, flies, and flying beetles. If another male of the same species enters their territory, they engage in an aerial sortie, spiralling high above the trees until the intruding butterfly is ousted.

Female butterflies live entirely different lives. Prior to mating they are often sedentary, remaining very close to the spot where they emerged from the pupa. After mating they seek places to lay their eggs, but usually fly only short distances between bouts of egg laying.

These differences in behaviour are reflected in their appearance – males need to be noticed, so are generally more colourful than females. The Adonis Blue Lysandra bellargus is a good example : the males are a brilliant iridescent blue colour, but the females are drab dark brown creatures – they spend most of their time crawling about on the ground amongst short grasses, looking for places to lay their eggs, but need to bask periodically so they can maintain their body temperatures. When basking on the ground, their drab colouration helps to camouflage them so they escape predation.

Adonis Blue Lysandra bellargus, male, Ballard Down, Dorset – Adrian Hoskins

Adonis Blue Lysandra bellargus, female, Ballard Down, Dorset – Adrian Hoskins

Roosting Behaviour

In cool or rainy weather butterflies are inactive, and thus particularly vulnerable to attack by birds and small mammals.

In tropical areas many species hide away beneath leaves, even when sunny, and only come into the open to undertake specific tasks such as feeding or reproducing. This behaviour is very widespread amongst the metalmarks ( Riodinidae ) and Spreadwing skippers ( Pyrginae ).

Eurybia molochina, ( Riodinidae ) hiding beneath a leaf in the Peruvian rainforest – Adrian Hoskins

In temperate zones, during periods of inclement weather, members of the Papilionidae and Pieridae normally roost beneath the leaves of herbaceous plants.

Pyrgines such as the Grizzled Skipper Pyrgus malvae usually roost at the top of dead flower-heads. The Dingy Skipper Erynnis tages behaves similarly, but takes things a stage further by wrapping it’s wings tightly around dead knapweed flowers, where it is almost impossible to see ( unless you are a very determined entomologist ! ).

Erynnis tages, ( Pyrginae ) roosting on a dead knapweed flower, Hampshire – Adrian Hoskins

Polyommatine Blues and Satyrines such as Small Heath, Marbled White and Meadow Brown tend to roost in a head-downwards posture at the top of grass heads. Pearl-bordered Fritillaries Clossiana euphrosyne and other Melitaeines adopt a similar tactic, often roosting on bracken fronds or on the flowers of rushes.

Such strategies may at first seem a little difficult to understand, as the butterflies are easily spotted. The probable explanation is that they are selecting sites where they are out of reach of nocturnal predators such as voles or shrews.

Clossiana selene, ( Nymphalinae : Melitaeini ) seed-head, Wiltshire, Kent – Adrian Hoskins

Hibernation

Hibernation is a process that depresses metabolism and energy consumption during the cold winter months. It ensures that energy is not wasted on fruitless searches for nectar and foliage in winter, and synchronises the spring reawakening with the time when flowers and fresh foliage reappear.

In temperate regions of the world most butterfly species overwinter as larvae. Others hibernate as eggs or pupae. A small number, including Inachis io, Polygonia c-album and Gonepteryx rhamni overwinter instead as adult butterflies. To successfully overwinter they need to find a place to hide where they are protected from the worst of the wind, rain and snow.

They may be in diapause for several months, and throughout this period they must remain undetected by birds. Accordingly they have evolved cryptic colours, patterns and unusual wing shapes that combine to provide them with effective camouflage.

The Brimstone Gonepteryx rhamni for example hibernates under bramble or ivy leaves and has wings coloured to match winter foliage. Its wings are also leaf-like in shape and have raised venation to simulate the veins of real leaves.

Gonepteryx rhamni, ( Pieridae ) hibernating beneath a bramble leaf, West Sussex – Adrian Hoskins

Many overwintering species such as the Peacock Inachis io, Camberwell Beauty Nymphalis antiopa and Large Tortoiseshell Nymphalis polychloros hibernate beneath logs or in hollow tree trunks; or in other dark places such as caves or animal burrows.

These species have evolved very dark ventral wing patterns which make it difficult for foraging birds to locate them in their gloomy surroundings.

A few species such as the Comma Polygonia c-album hibernate openly, hanging from tree branches or amongst piles of leaf litter on the forest floor. Their dark marbled patterns and strange angular wing shape provides them with an extremely effective dead-leaf disguise.

Polygonia c-album, ( Nymphalidae ) hibernating beneath a branch, West Sussex – Adrian Hoskins

Lifespan

The whole lifecycle from egg to adult can take just 3 weeks to complete in many tropical species. In temperate regions the lifecycle of the summer generation may be complete within 6 weeks, but many species only produce a single generation in a year. In sub-arctic zones some species such as Parnassius eversmanni, Boloria natazhati and Oeneis alpina take 2 years to complete the lifecycle.

The lifespan of butterflies varies considerably from one species to another. Captive butterflies, if fed regularly can live for several weeks. Wild butterflies are subject to predation and the extremes of climate, so while some may have the potential to live longer, in practice the average lifespan is just 7 or 8 days.

There are however several notable exceptions to this general rule. Some butterflies, e.g. Monarchs, Commas and Tortoiseshells, hibernate as adults, and these species often live for several months. The longest lived European species are the Brimstone and Peacock – both emerge in early July, and often survive until the following June.

Certain tropical species are also capable of surviving for equally long periods. In Central & South America female Heliconius butterflies sequester pollen from Psiguria, Anguria and Gurania flowers in the rainforest. The pollen collected from the flowers is processed by the females to extract amino acids which increase longevity and enable them to produce eggs for up to 9 months.

Other tropical species e.g. the Satyrine Taygetis mermeria and certain Ithomiines, Heliconiines and Danaines are able to extend their lives by aestivating during the dry season, and can live for up to 11 months.