Since then the human population has grown and has become increasingly wasteful and greedy. Wild places have consequently diminished in size and become increasingly fragmented and isolated.

Shrinking habitats mean smaller butterfly populations. As breeding sites become smaller and more isolated, gene interchange reduces to insignificant levels.

Butterflies then lose their adaptability and become become dependent on highly localised and specialised habitats. The isolated populations of Papilio machaon in England e.g. can only now survive at a handful of flooded Norfolk fenland sites, whereas in mainland Europe where habitats are larger and less isolated, the species breeds over a very wide area and utilises a broad range of habitat types.

Habitat destruction across the world is caused almost entirely by human activity. Urban expansion has the greatest impact, but governmental policy on farming, forestry and road planning also has a very profound effect on the distribution and abundance of butterflies.

The destruction of the rainforests

In excess of 10000 square miles ( 2.6 million hectares ) of Amazon rainforest is deliberately burnt down every year to clear land for soya and oil palm plantations.

The notion that vegetarianism is beneficial to wildlife is utterly absurd, as wonderful rainforests that support billions of animals and plants are wantonly destroyed, burnt down and replaced with these lifeless and sterile plantations.

In addition to the gargantuan areas of land destroyed to make way for plantations, vast expanses of forest are devastated by slash and burn farming. This normally occurs on a smaller scale as it is carried out by small farming communities rather than by multi-national companies.

Nevertheless it accounts for the loss or severe degradation of many thousands of sq kms of rainforest every year. Land which once supported 750 species of trees, 1500 species of flowering plants, 500+ species of birds and perhaps 1000 species of butterfly, is cleared to make way for cattle ranches. The bounty is short-lived however.

The resulting pastures are poor in nutrients, and only capable of supporting cattle at very low densities. The pastures are burned annually to promote new grass growth and to destroy cattle parasites. The fires rage uncontrolled, devastating vast areas of land.

The deforested land is much hotter and drier than the rainforests – consequently the average temperature of the entire region rises and the humidity falls dramatically. This causes major changes in the vegetation structure of the remaining areas of forest, leading to reduced biodiversity even in protected areas.

Please support rainforest conservation :

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All stages of the lifecycle are threatened by parasitoids : creatures that feed on other organisms, and ultimately bring about their death. Note that parasitoids shouldn’t be confused with parasites – which unlike parasitoids do NOT bring about the death of their hosts.

Egg parasitoids

Many butterfly species fall victim to tiny wasps that inject their eggs into the soft newly laid butterfly eggs. When the wasp grubs hatch they feed on the organic matter within the egg, killing the potential caterpillar. The adult wasps emerge a few days later and use their mandibles to cut minute exit holes to make their escape from the eggs. In some cases as many as 60 microscopic wasps can emerge from a single butterfly egg.

South American Caligo Owl butterflies are parasitised by a tiny Trichogrammatid wasp that rides from place to place on the hindwings of female butterflies. When the butterfly settles momentarily to lay her eggs the wasp hops off, injects it’s own eggs into those of the butterfly, and then hops back onto the butterfly’s wing in time to be transported to the next egg laying site !

Caterpillar parasitoids

Throughout their lives caterpillars are very vulnerable to attack from parasitoids. Studies in Britain have revealed that with most Lepidoptera species, about 80% of larvae are attacked by parasitoid wasps or flies. In the case of the Marsh Fritillary Euphydryas aurinia between 90-95% of larvae are parasitised by the wasp Apanteles bignelli in certain years.

Wasps such as Apanteles, Amblyteles, Netelia, Ophion, Protichneumon and Ichneumon, and flies suchs Tachina, Gymnochaeta and Gonia spend their larval stage within the bodies of caterpillars.

The adult wasps and flies inject their eggs into the caterpillar’s body by means of a long sting-like ovipositor, or in some cases lay their eggs on leaves which are ingested by the caterpillar.

Hawkmoth larva Eumorpha fasciatus, Peru – Adrian Hoskins

The larva of Eumorpha fasciatus illustrated above has been parasitised by a wasp that injected it’s eggs into it. When the wasp grubs are fully grown they break out through the skin of the larva and form their papery white cocoons. The larva shrivels and dies. A few days or weeks later the adult wasps emerge from the cocoons and search for another larva to parasitise.

The larva of Hasora badra shown below has been parasitised by an Apanteles species – a total of 67 wasps emerged from the cocoons which surround it.

Common Awl Skipper Hasora badra surrounded by Apanteles cocoons – SoonChye

Defence strategies

 ( see also Larval survival mechanisms )Many larvae are equipped with thick coats of hair, or fierce-looking spikes that make it difficult for parasitoids to settle on them. Others, e.g. those of the Puss moth Cerura vinula and the hawkmoth Isognathus leachi are armed with long whip-like structures which they use to drive off any wasp or fly that attempts to attack.

Isognathus leachi, Fazenda Rancho Grande, Rondonia, Brazil ï¿½ Adrian Hoskins

Unfortunately in practice it the whip is not very effective as a defence, as Paul Bertner describes :”We spotted the Winthemia tachinid fly circling around the Isognathus larva. The extremely long tail of the larva appears to serve a defensive function.

As the fly landed close to the rear, the larva would flick its tail, dislodging the fly to prevent it from ovipositing. The fly undeterred walked up the body until it was close to the head and out of range of the tail where it began to lay eggs. It seemed to prefer the posterior end of the larva for some reason as it kept on trying to move back there, perhaps laying too close to the front might kill the larva faster and thereby not leave enough time for the fly grubs to mature, whereas the rear of the larva may not house such vital organs to be destroyed by the grubs”.

The long orange ovipositor of the fly can be seen quite clearly in the photo below :

Tachinid fly Winthemia sp, injecting eggs into an Isognathus larva – Paul Bertner

Some flies such as Sturmia bella don’t oviposit directly on the larva. Instead they lay their eggs on its foodplants. These are ingested and pass into the larva’s gut. After the eggs hatch the resulting grubs consume the larva’s flesh, but leave the vital organs alone, allowing the larva to continue to live and grow. Eventually when the parasitoid grubs are mature and ready to pupate they eat the vital organs. They then pupate either within the body of the dying larva, or eat their way out of it’s skin and pupate externally.

Nematode worms

The larvae of many butterflies and moths are attacked by entomopathogenic nematode worms from the family Mermithidae. The tiny juvenile worm is sometimes unintentionally ingested by a larva as it browses on leaves. In other cases it may enter via the larva’s anus. The larva depicted below is that of Cyclosia papilionaris – a moth in the family Zygaenidae. It has been parasitised by a single Mermethid worm which has fed and grown within it for several days. When the worm is fully grown it exits the larva, which shrivels and dies.

Cyclosia papilionaris with parasitic worm, Cambodia – Dani Jump

Parasitoids of pupae

Other wasps attack newly formed butterfly pupae while the skin is still soft and easily punctured. An example is the beautiful metallic green wasp Pteromalus puparum, which attacks pre-pupal larvae and newly formed pupae of Pieris brassicae. The entire lifecycle of Pteromalus takes place within the butterfly pupa, and the tiny wasps emerge in dozens after making exit holes in the pupal skin.

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.

Parasites

Parasites are creatures which feed upon other organisms, but unlike parasitoids they do not cause the death of their hosts. In the case of Lepidoptera, they generally affect the adult butterflies and moths rather than caterpillars.Certain butterflies, particularly males of Meadow Brown Maniola jurtina, Marbled White Melanargia galathea, Common Blue Polyommatus icarus & Small Skipper Thymelicus sylvestris are commonly parasitised by tiny red mites Trombidium breei, which normally attach themselves to the thorax or legs of the butterfly. They transfer from host to host when the butterflies alight to nectar at flowers.

Melanargia galathea with parasitic red mites Trombidium breei attached to thorax – Adrian Hoskins

Studies have shown that the Trombidium mites have no detectable effect on the flight performance, orientation ability or lifespan of the butterflies. In New Zealand however there is another species of mite called Dicrocheles, which does have an injurious affect on adult Noctuid moths. They infest the “ears” on the wings of the moths. Apparently, in areas where there are no predatory bats, the mites attack both ears, making the moths go completely deaf. But in areas where bats thrive, the mites seem to only attack one of the ears, so the moth is still able to detect the bat’s acoustic pulses and take avoiding action. The theory goes that “if the moth cannot hear the bat, both the moth and the mites will almost certainly be eaten, so they make sure to keep one ear functional”.

In South American cloudforests, adult Glasswing butterflies Greta andromica, are often attacked by Ceratopogonid midges, which feed on the blood in the butterfly’s wing veins and eyes. The same midges also attack larvae, sucking their haemolymph.

Pseudoscorpion hitch-hikers

Close examination of recently emerged butterflies can sometimes reveal the presence of very tiny scorpion-like creatures clinging by their pincers to the legs or antennae. These “pseudoscorpions” are carnivorous, typically feeding on mites, insect eggs and young larvae, but don’t harm the butterflies. They simply hitch a lift on butterflies and other insects, using them as transportation to enable them to disperse to new habitats.

One tactic they use is to ambush a fully grown caterpillar, grabbing its spines or head horns with their powerful pincers. When the pincers “bite”, the pseudoscorpion becomes quiescent.  After a few hours the caterpillar pupates, and the pseudoscorpion remains attached to the shed larval skin, which itself remains attached to the base of the pupa. Eventually the butterfly emerges from the pupa, and the pseudoscorpion then scuttles on board, grabbing hold of its antennae or legs. This causes the butterfly to take flight. Sometime later, when the butterfly lands in a suitable place, the pseudoscorpion drops off, and colonises it’s new found habitat. Pseudoscorpions are related to spiders, mites, scorpions and harvestmen. Their hitch-hiking behaviour is known as “phoresy”.

Pathogens etc

Fungal and viral diseases are most prevalent in cool damp conditions and cause the death of many hibernating larvae and pupae in temperate regions. They also affect the early stages of tropical species, particularly during the rainy season. Living caterpillars are subject to infection by many fungi including Cordyceps, Metarrhizium and Beauvaria.

Caterpillars are often attacked by nuclear polyhedrosis viruses, granulosis viruses and cytoplasmic polyhedrosis viruses. Affected larvae become limp, darken in colouration, and produce liquid faeces prior to death. The condition is known as wilt disease, and is highly infectious.

The larva illustrated below may look as if it is dead and going mouldy but in fact it was very much alive, crawling rapidly over the leaves of a small bush deep in the Amazonian rainforest. The larva has been infected by an entomophagous fungus. Its rapid movement is an example of how normal behaviour is altered in an infected host. Some entomologists speculate that this type of behavioural change is a self-sacrifice survival technique, whereby an individual that is doomed to die will draw attention to itself and in doing so divert the attention of predators away from its healthy and slower moving cogeners. Whether insects are capable of such altruistic acts is of course debatable!

unidentified moth larva ( ref 016 ), Rio Madre de Dios, 400m, Peru – Adrian Hoskins

Despite the massive losses ascribable to predators, parasitoids, viral / fungal diseases and physical causes ( rain washing away eggs, caterpillars falling from their foodplants etc ), enough offspring generally survive to maintain reasonably stable populations.

The Balance of Nature

Invertebrate predators possess varying degrees of intelligence and quickly learn how to overcome the huge variety of defence mechanisms employed by their prey. It is known that some birds can pass on learnt behaviour to their offspring, so their ability to locate and butterflies and their larvae increases with each passing generation. Many birds also possess empathic learning abilities, so an individual can learn to avoid toxic butterflies simply by observing another bird vomiting or suffering muscular spasms after regurgitating one.

Luckily butterflies have a couple of advantages over birds. Firstly, a high percentage of species are polyvoltine ( producing several generations per year ). This rapid rate of reproduction allows them to recover their numbers rapidly even after major losses of population. Secondly, butterflies and moths intrinsically produce high genetic diversity. These two factors result in an ability to evolve rapidly, the consequence being that the battle between birds and butterflies has become a closely run race. Birds catch enough caterpillars and butterflies to feed themselves and their offspring, but at the same time enough butterflies survive to ensure that both predator and prey can continue to co-exist. This is the so-called “balance of nature”, an ongoing evolutionary battle between predator ( or parasitoid ) and prey.

Short term variations in this balance are mainly attributable to seasonal fluctuations in climate :Caterpillars are cold-blooded, and need warmth to induce feeding activity. Thus in a cool spring they take longer to develop, so more get eaten by birds, and more get attacked by parasitoids. In the case of nocturnal larvae the opposite is the case – cloudy weather stops night temperatures from dropping and increases the caterpillar’s growth rate. So in poor weather they develop more rapidly and fewer get attacked by parasitoids.

Strictly speaking, predators and parasitoids should not be considered as enemies of butterflies. They could perhaps instead be thought of as Nature’s way of preventing butterfly populations from getting out of control – if they were not kept in check, the populations would rapidly expand and would quickly deplete all available food resources, ultimately leading to their own demise.

A butterfly may be capable of laying up to 500 eggs. On average however only about 100 will be laid, as many females die before they are able to lay all their eggs. Perhaps 95 of those eggs will hatch. 85 of the resulting caterpillars are likely to be killed by birds, wasps, spiders or parasitoids, leaving just 10 to reach pupation. Studies have found that over half of all wild pupae will be eaten, be killed by parasitoids, or die from desiccation, fungal attack, or other causes.

The net result is that the eggs laid by a single butterfly will, averaged over several years, result in only about 4 adults per generation. As many as half of the adult butterflies will be killed before they mate or are able to lay eggs. So, despite the ability to produce those 500 eggs and the potential of 500 butterflies, just 2 butterflies will result from each brood of eggs. With luck one of these will be a male and the other a female, and another batch of eggs will be produced.

Avian predators

Throughout the world, adult butterflies are killed in vast numbers by birds including sparrows, tits, thrushes, robins, orioles, jays, grosbeaks, crossbills, flycatchers, jays, tanagers and jacamars.Various studies have provided statistical data on avian predation. One study for example revealed that 160 out of 697 examined specimens ( 23% ) of Ascia monuste bore beak marks on their wings indicating that they had been attacked by birds, but had escaped or been rejected. This figure does not of course include the specimens that were actually eaten.

Another study of the feeding behaviour of ( captive ) rufous-tailed jacamars Galbula ruficauda in Costa Rica found that when 1679 butterflies of 133 species were offered to the birds approximately 5% were classed as failed attacks. 35% were ignored or sight-rejected. About 20% were attacked, captured and then taste-rejected. The remaining 40% were attacked, killed and eaten. The species offered to the birds were categorised according to colour. Those that were sight-rejected or taste-rejected generally were aposematically coloured species, while those that were devoured tended to be the less colourful or cryptically patterned butterflies.

It is apparent from the many studies carried out that at least 50% of wild butterflies are killed and eaten before they are able to mate and reproduce. Some are attacked when they are emerging or drying their wings prior to their first flight. Others fall victim when basking on the ground or visiting flowers, although many are lucky to escape with nothing more than a peck taken out of a wing.

Birds and other vertebrate predators rely primarily on sight to locate prey, so butterflies and moths have evolved numerous visually mediated means to avoid attack. These include passive defence mechanisms e.g. camouflage, disguise, mimicry, warning colouration and transparency. Sometimes passive mechanisms fail, and a butterfly will find itself under direct attack. At this stage secondary or active mechanisms come into play.

The flowchart below illustrates many of the survival strategies which butterflies have evolved to defend themselves against attacks by insectivorous birds :

Spiders and predatory insects

Although birds are probably the main predators, adult butterflies also have to contend with spiders, wasps, dragonflies, robber flies and crickets. In warm climates they are also attacked by mantises and numerous other arthropods.

It is common to see butterflies caught in the grip of crab spiders, which lie in wait among flowers, ambushing any butterflies that visit them for nectar. Butterflies also often wander into the webs of orb spiders. The smaller weaker butterflies such as Polyommatus, Lysandra and Coenonympha invariably become entangled and are quickly wrapped up in silk for later consumption. Larger butterflies however such as Vanessa and Argynnis are often able to struggle free before being pounced upon by the owner of the web.

Close examination of adult butterflies often reveals a give-away reticulation pattern across the wings, marking the places where loose wing scales have become detached and left behind on the sticky threads of the web. It is even possible that wing scales have evolved to be easily detachable as a survival mechanism.

Hornets and wasps are major predators of butterflies in mid-late summer. By way of example, in July 2009 at Alice Holt forest in England I watched a hornet Vespa crabro chasing after Ringlets and Meadow Browns. It failed to catch any, but moments later, when I was trying to photograph a White Admiral nectaring at bramble, another hornet suddenly shot down and snatched the butterfly from the flower. In a split second it had grabbed it, bitten off its forewings, and used its hindwings to wrap the paralysed butterfly up into a tight ball. Seconds later, carrying the parcel in it’s mandibles, it flew up to its nest at the top of a small oak. Once there it would have chewed the butterfly into a pulp and regurgitated it to feed its developing grubs – adult hornets are strictly vegetarian, feeding on nectar and fruit.

Broad-bodied Chaser Dragonfly Libellula depressa commonly preys on butterflies – Adrian Hoskins

In southern Britain one of the commonest butterfly predators is the spider Enoplognatha ovata, a member of the Theridiidae. This small species traps summer butterflies which fly into the sticky strands of an untidy web which it spins on grass-heads and wild flowers. I made a brief study of predation at Magdalen Hill Down in Hampshire in July 2009 and estimated that about 5% of the population of Chalkhill Blues Lysandra coridon fell victim to this spider.

Theridiid spider Enoplognatha ovata, devouring Chalkhill Blue Lysandra coridon – Adrian Hoskins

Hunting spider Pisaura mirabilis – Adrian Hoskins

Male hunting spiders Pisaura mirabilis attack butterflies that settle on low herbage. They wrap their victims tightly in silk and present them to the female spider as a courtship gift. While the spiders are mating the female feeds on the butterfly.

Crab spiders are a major predator of small butterflies. An individual will sometimes spend several days sitting motionless on a flower head, waiting it’s next victim to fly in. The peripheral vision of the spider is poor, so much so that it is possible for a butterfly to settle alongside it without being noticed. If on the other hand it is unfortunate enough to walk across the spider’s field of forward vision, the arachnid will move immediately and stealthily towards the butterfly and seize it with its powerful pincer-like forelegs. The spider then bites the butterfly on the neck, injecting it with a paralysing venom which incorporates enzymes that liquefy the victim’s internal tissues.

The photo below illustrates a Chestnut Heath Coenonympha glycerion that has been ambushed by the crab spider Thomisus onustus.

This remarkable spider has a chameleon-like ability to change colour to match it’s surroundings. It can be white, yellow, pink or variegated in appearance. The change of colour takes about 2 or 3 days to complete however, so it’s common to find a spider on the “wrong” coloured flower.

Coenonympha glycerion, ambushed by crab spider Thomisus onustus – Peter Bruce-Jones

Altinote dicaeus attacked and eaten by a cricket in Manu cloudforest, Peru – Adrian Hoskins

Predators of caterpillars

Butterfly and moth larvae are taken in huge numbers by predators. A study of predation on Pieris rapae estimated that 52% and 63% of 1st / 2nd instar larvae were eaten in 2 consecutive years by invertebrate predators including Carabid beetles, Hemipteran bugs, wasps, mites and spiders. The same study estimated that as many as 22% of older Pieris rapae larvae were taken by birds, which of course have to feed not only themselves but their offspring at the nest.

Birds, reptiles, amphibians and small mammals rely primarily on sight to locate prey. Lepidopteran larvae have correspondingly evolved a battery of visually directed defence mechanisms to reduce the likelihood of being eaten. These include camouflage, disguise, mimicry, aposematic / diematic colouration and the use of stinging spines to ward off attacks.

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 alternative solutions. The larva of the Puss moth Cerura vinula for example is armed with long “tail whips”. If attacked it arches it’s body into an aggressive posture and uses the whips to thrash the attacker to drive it away.

Swallowtail larvae are palatable to birds and employ cryptic colours and patterns as a first line of defence. If discovered however they activate secondary defences. Many of them are marked with a pair of “false eyes” on the thoracic segments, so they inhale air through the spiracles and puff up these segments to emphasise their threatening appearance. This is often enough to deter avian and reptilian predators. Molestation by insect predators and parasitoids elicits a different response from the larvae. In this instance they evert a fleshy structure behind their heads called an osmaterium. 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.

The larvae of species such as the Peacock butterfly Inachis io, the Tiger moth Arctia caja and the Fox moth Macrothylacia rubi rely on escape tricks. If molested they simply roll into a ball and drop to the ground. 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 they are molested they release grip on the sprig and drop instantly from a bungee-cord of silk. They dangle at the end of this until the attacker has moved on. After a while they haul themselves back up, consuming the silk thread as they does so.

The larvae of many members of the family Lycaenidae defend themselves by forming a beneficial association with ants. The anal segment of the larva houses a dorsal honey gland which exudes a sweet tasting fluid which ants love to drink. The larvae thus find themselves constantly attended by dozens of ants, the presence of which deters predators & parasitoids from attacking. Many species take the association a stage further and are carried by the ants into their nests where they feed on ant grubs, aphids or fungi. The ants don’t attack the larvae as the latter are able to mollify them, either by using chemical deterrents or by stridulating to produce an “appeasement song”. Research on several Hairstreaks and Blues in Europe has demonstrated that their larvae and pupae are able to generate an audible “chirp” which deters ants from attacking.

Caterpillar defence mechanisms are discussed more fully in the lifecycle section.

Heteropteran bugs such as this species from Peru often attack and eat larvae – Adrian Hoskins

Adders and other juvenile snakes eat diurnal butterfly and moth larvae, as well as beetles, spiders and nestling rodents. Click here for more about the Adder – Adrian Hoskins

Common Toads are major predators of European caterpillars such as Ringlet and Speckled Wood. Click here for more about the Common Toad – Adrian Hoskins