Some butterflies, including the Hamadryas Crackers and Heliconius Longwings, can detect sound using an “ear” near the base of the underside of their wings. The ear, visible only under a powerful microscope, takes the form of a funnel-shaped sac covered with a very thin membrane. This membrane vibrates in response to high-frequency sound, stimulating nerve cells called scolopidia, which send messages to the butterfly’s brain.

Hamadryas butterflies use their ears to detect crackling noises made by territorial males, produced by twanging two tiny prongs on the tip of the abdomen against bristles on the valvae.

Males habitually bask on tree trunks, waiting to intercept passing females. It has been speculated that the sound might deter competing males from occupying the same territory, but a single tree trunk will often host 3-4 males perching in close proximity. It seems more likely that the sounds act as a trigger to initiate responses from females during courtship.

Kathleen Lucas of the University of Bristol used a laser beam to scan the membrane of the eardrum of Morpho peleides (= helenor). She found that lower frequencies between 1000 – 5000 Hz caused vibrations to focus on a spot on the outer membrane, but frequencies above 5000 Hz caused the entire membrane to vibrate, including the “fried egg” dome structure arrowed in the photo. Moth ears respond equally to all frequencies, but Morpho butterflies seem able to differentiate between low and high-pitched sounds. Lucas speculated that this could help the butterflies figure out if birds are about to attack. If, for example, they could tell apart the sounds of flapping bird wings and those of bird song, it might trigger different escape responses by the butterfly.

Some scientists believe that when butterflies first evolved, they were nocturnal, and their ears originally served to detect and avoid predatory bats. Bats emit acoustic pulses when flying at night and use their highly sensitive ears to detect the echo reflected back by solid objects. This way, they avoid hitting unseen obstacles and are able to locate moving prey in the dark.

Noctuid moths (and certain other groups) are able to hear a bat’s acoustic pulses. The frequency and volume enable the moth to detect how far away the bat is. Furthermore, the relative positions of the moth’s hearing organs enable it to determine the direction of approach. The moth initially reacts by steering away from the bat, but if it gets within striking distance, the moth instantly dive-bombs to avoid being eaten.

Nerve cells similar to those in the “ears” are also found in enlarged veins at the base of the forewings of many butterflies. These are particularly well-developed in Satyrines such as Oressinoma, Maniola, Pararge, and Hipparchia, all of which react instantly to the sound made as dry leaves are crunched underfoot or to the noise made by the shutter of a camera.

Flight

Insect flight evolved at least 90 million years ago, long before it appeared in birds or bats, so its original function must have been for something other than predator avoidance. The most likely explanation is that it evolved to enable insects to reach food sources by the most direct and rapid route. What is not currently understood is the method by which the evolution took place.

Some have suggested that wings evolved from nodes on the thorax. Another possibility is that they may have originally appeared as short flexible thoracic hairs, akin to cat whiskers, which enabled the insects to find their way through burrows. Once insects began to climb plants, they may have evolved further as a way of cushioning the landing of falling insects and ultimately as a means of easier dispersal, mate location, and food location.

Skippers tend to have a buzzing moth-like flight, and other small butterflies such as Lycaenids and Riodinids need to beat their wings rapidly to propel themselves through the air. Larger species such as Nymphalids, Pierids, and Papilionids fly by a combination of flapping and gliding. When gliding, the wings are held so as to create a concave under-surface, producing a parachute effect which slows the rate of descent. These larger species also make use of thermals to gain or maintain height when gliding above the forest canopy or when migrating.

Males of many species adopt a “perch and wait” mate locating strategy and need to be able to take flight rapidly to intercept potential mates. Examples include Skippers (Hesperiinae), Metalmarks (Riodinidae), and Graylings (Satyrinae). These species often tend to have triangular forewings with a particularly thick and straight costa. The springy qualities of the costa, in combination with their powerful flight muscles, enable them to accelerate rapidly at takeoff.

Other species, such as Whites (Pierinae), Swallowtails (Papilionidae), Blues (Lycaenidae), and Morphos (Morphini), adopt a “patrolling” mate location strategy. Thus they have no need for such rapid acceleration. They tend therefore to have rounder and less robust wings, which are larger in relation to their thinner and less muscular bodies. Consequently, their flight is much lazier.

Eurybia species, probably molochina, Madre de Dios, Peru – Adrian Hoskins

In the neotropics, Eurybia butterflies ( Riodinidae ) habitually spend long periods resting upside down and with wings spread open, beneath the leaves of low growing vegetation. Flight analysis has shown that by doing so they are able to take off much more rapidly than they could if they rested the “right” way up. From their hiding place they keep a watchful eye on passing insects.

Periodically they dash out to intercept and investigate other butterflies, but instantly return to settle under a nearby leaf. The speed of flight is remarkable, and the degree of agility apparent when they fly into the vegetation, flip upside-down and settle under another leaf is quite amazing to behold.

Thermo-regulation

Butterflies are cold-blooded. If they are too cold they cannot fly. If they get too hot they become dehydrated and die. They have no internal means of regulating their body temperature, so they need to use behavioural strategies instead.

In cool conditions butterflies need to raise their body temperatures before they are able to fly. To do so they use a technique known as dorsal basking, whereby they use the upper surface of their wings as solar panels to absorb heat and give them energy. Often they settle to bask on pale, heat-reflecting substrates such as stones, tree-trunks or patches of bare ground.

Heat is reflected back from the substrate and absorbed by the dark undersides of the wings, speeding up the warm-up process. Males in particular use this method, to ensure that they always have sufficient energy available to enable them to instantly fly up to intercept passing females.

Some butterflies, such as Clouded Yellows, Graylings & Green Hairstreaks, always keep their wings closed when at rest, and adopt another technique known as lateral basking. In cool conditions they bask by tilting their wings over to one side, so as to present the maximum area of wing surface to the sun. Conversely, when they get too hot, they tilt in the opposite direction so that their wing surfaces are parallel to the sun’s rays, and present the minimum surface area to the sun.

Grayling Hipparchia semele, lateral basking at Arnside Knott, Cumbria, England – Adrian Hoskins

The Whites, Blues and Coppers have wing surfaces which reflect, rather than absorb solar energy. Consequently they bask with their wings half open, so that the heat produced by sunlight falling on the dark thorax is contained within the “cage” of the half-open wings, rather than being dispersed on the breeze. This behaviour is called reflectance basking.

Another method used to raise body temperatures is “shivering”. Many Nymphalid species, including Peacocks, Small Tortoiseshells & Red Admirals prepare themselves for flight by rapidly shivering the wings ( which are held closed during this process ). Even on the coolest day, a minute or two of this activity generates enough friction to heat up the thoracic muscles enough to enable them to fly short distances. Nocturnal moths often adopt the same technique.

Butterflies can only operate within a limited temperature range, so on hot days they need to find ways of keeping cool. Forest-dwelling species simply hide beneath leaves, while species that inhabit open areas often fly into bushes to seek shade, or enter rabbit burrows.

On this page you will find a selection of ultra-high magnification SEM images depicting butterfly wing scales.

Cleopatra Gonepteryx cleopatra ( Pieridae: Coliadinae ):

A group of scales from the orange part of the wing of Gonepteryx cleopatra – Rob Lineton

Butterfly wing scales are laid out in neat rows like the tiles on a roof. Some scales like those from the orange area of the wing of Gonepteryx cleopatra are shield-shaped, others can be shapes like hearts, spears or very long thin hairs, depending on their location and function.

A single wing-scale of Gonepteryx cleopatra – Rob Lineton

Under high magnification it can be seen that the scales are constructed from about 20-40 parallel ribs, each linked by a series of tiny cross bars. The spaces between the ribs and cross bars diffract light to different degrees and thereby produce the myriad of hues which form the wing patterns.

SEM image showing a tiny section from a wing scale of Gonepteryx cleopatra. The vertical ribs are connected by tiny rods, each covered with spore-like protuberances – Rob Lineton

2-tailed Pasha Charaxes jasius ( Nymphalidae: Charaxinae ):

A group of scales from Charaxes jasius. These are longer and narrower than those of Gonepteryx cleopatra, and show evidence of forking in a few places – Rob Lineton

Charaxes jasius. Under extreme magnification it is apparent that these scales do not have the tiny spore-like protuberances found in G. cleopatra Rob Lineton

Venation

All butterflies and moths ( except Plume moths ) have 2 pairs of overlapping wings, each comprised of a very thin double membrane with rigidity supplied by a network of tubular veins which radiate from the base of the wings. The pattern of veins is different for every genus of butterfly, and is one of the main criteria used by taxonomists when classifying butterflies.

Vein structure of a transparent Satyrine butterfly Haetera piera – Tony Hoare

Scales

The wing membranes are transparent, but are partially or fully covered in a dust-like layer of tiny coloured scales. Each scale comprises of a flat plate arising from a single cell on the wing surface.

The scales vary considerably in shape, some being rectangular, while others are shaped like tear-drops or plumes. An individual scale might typically measure about 50 microns across ( 1/20 of a millimetre ) and be 100 microns long, although many are hair-like, and are very much longer.

There can be as many as 600 individual scales per sq millimetre of wing surface, although in certain genera such as Acraea, Aporia and Parnassius the density is considerably lower, giving the wings a translucent appearance. In some tropical genera such as Ithomia, Lamproptera and Cithaerias the scales are absent from large areas of the wings, resulting in almost complete transparency.

Catoblepia berecynthia ( Peru ), wing scales, magnification x10 – Adrian Hoskins

Pigmentary scales

Pigmentary scales are mostly flat. Their color is the result of the presence of melanins, pterins, and other chemical pigments, most of which are sequestered from the larval food plants and passed to the adult butterflies. The pigments account for the basic colors found in butterfly wings – black, red, and yellow. The juxtaposition of the various colored scales, and the amount of pigment they each contain, can create the illusion of additional colors such as orange, cream, and green.

In some species such as the Orange tip Anthocharis cardamines, the mottled green markings on the underside are an illusion caused by having a finely balanced mixture of yellow and black scales. Subtle variations in scale pigmentation and density can create illusions such as texture or shading, which help to give the wings of some butterflies a 3-dimensional appearance.

Structural scales

The fiery hues of Lycaena Coppers, the golden-yellow of Troides Birdwings, the glittering metallic greens of Caria Metalmarks, and the dazzling blues of the South American Morpho butterflies are produced by the refraction, diffraction, and interference patterns of light as it strikes or passes through the semi-transparent structural scales.

In the case of diffraction, light is broken up into lighter or darker bands after passing through a lattice of microscopic bubbles or slits within the scales. Refraction, on the other hand, is where light is broken up into its constituent rainbow colors as a result of passing through prismatic ridges on the surface of the scale.

Interference patterns are the result of light passing through clear layers of varying density, and being reflected back in such a way that the colors change according to the angle of view. Examples of such iridescent color are found in many butterflies, but are particularly striking in neotropical Doxocopa butterflies, where a band of color can change from electric blue to vivid turquoise or dazzling silver as sunlight strikes the wings at different angles.

Androconia

Androconia are found mainly on male butterflies.

They usually exist as slightly raised dark streaks or patches on the forewings and often have a mealy appearance. At the base of the androconia are tiny sacs containing scent (pheromones). The scent is disseminated via tiny hairs or plumes on the edges of the scales and used to entice females to copulate.

Male androconia can also take the form of tufts (e.g., on the hindwings of Morpho and Charaxes) or can be found in androconial folds such as found on the hindwings of Papilionidae or the costal fold of Pyrginae. In the Danaini and Ithomiini, they occur as “hair-pencils”.

These can either take the form of extrusible organs at the tip of the abdomen or occur as long “hairs” on the hindwings. In some species, e.g., Lycorea, the abdominal organ is brushed against androconia on the hindwings to collect pheromones. These are later disseminated by expanding the tufts in the presence of females.

Androconia can also occur as “stink-clubs” in the genital opening of female Battus, Parides, Troides, Ornithoptera, and Heliconius butterflies, and in certain moth families, e.g., Saturniidae, Lasiocampidae, and Lymantridae.

Large Skipper Ochlodes venata, England – Adrian Hoskins

The dark diagonal patch on forewings of the male Large Skipper illustrated above are composed of hundreds of androconial scales. These disseminate pheromones that can be detected by females during courtship. As the male ages the strength of his pheromones diminishes, thus by analysing the strength of the pheromones a female can assess the age and virility of a potential mate.

Plume moths

Plume moths from the families Pterophorinae and Alucitidae have no wing membranes. Instead their fore and hind wings each consist of rigid veins edged with dozens of long thin feathery scales giving rise to the common name of “plume moths”. 

There are 186 species of Alucitidae worldwide, many of which have only been discovered in the last 20 years. The name of the moth depicted below, Alucita hexadactyla translates as “20 fingers” but is a misnomer: Alucitidae actually have 24 feathery plumes ( some are hidden in the image below ).

Many-plumed moth Alucita hexadactyla, Hampshire, England – Adrian Hoskins

The Pterophorinae are similar anatomically but are distinguished by their long, spurred hind legs and the odd resting posture in which the wings are rolled up and held at an angle of 90 to the body.

Common Plume moth Emmelina monodactyla ( Pterophorinae ), England – Adrian Hoskins

Thorax

The thorax consists of 3 body segments which are fused together, forming a chitinous cage which contains the flight muscles, and acts as an anchor point for the legs.

Within the thoracic cavity of flying insects are very powerful muscles which lever on the wings. The rapid expansion and contraction of the muscles causes the wings to rise and fall at rates of up to 1000 beats per second in bees and hoverflies, and about 200 beats per second in hawkmoths.

Amongst the butterflies, Skippers have the fastest wing beats. Their wings whirr audibly at a rate of about 20 beats per second as the butterflies dart rapidly from place to place. Other butterflies such as Swallowtails, Pierids and Satyrines can only manage about 5-10 beats per second. Slower still are the Ithomiines which have very deep beats at about 4 per second. Slowest of all are the Caligo Owl butterflies which struggle to achieve more than 2 or 3 beats per second.

Legs

All adult butterflies have 3 pairs of legs, except in the Nymphalidae and in males of certain other groups, where the front pair are reduced to brush-like stumps and modified as chemoreceptors.

The tibia of each leg has a subgenual ( under the knee ) organ, which detects and amplifies small vibrations. This alerts butterflies to ground vibrations caused by the approach of animals or birds, enabling them to respond instantly to danger. In most cases they take flight flight, but some species such as the Peacock Inachis io and Bullseye moths Automeris randa react by suddenly flashing open their wings to display “false eye” markings that startle the predator.

The tibia on the forelegs of Pieridae, Hesperiidae, Papilionidae and Lycaenidae are often equipped with a flexible spur through which the antennae can be drawn for cleaning.

The spur also functions as a spike with which a female can puncture the cuticle of a leaf, causing it to bleed minute quantities of chemicals. The butterfly then checks the chemical composition of the leaf, using olfactory sensors on her legs and feet. This enables her to determine whether the plant is of the correct species to support her offspring. Thus a female will spend long periods flitting from leaf to leaf, “tasting” each one with her feet to assess its suitability prior to egg laying.

Wood White Leptidea sinapis, Surrey, England – Adrian Hoskins

The Wood White Leptidea sinapis, like all Pieridae species, has 6 fully functional legs. Males of some Pieridae such as the Brimstone Gonepteryx rhamni often rest with the forelegs held tight against the body, so at first glance can appear to have only 4 legs.

Euphydryas aurinia, a Nymphalid with only 4 functional legs in both sexes – Adrian Hoskins

Abdomen

The abdomen contains the digestive system, breathing apparatus, a long tubular heart, and the sexual organs. The abdominal exoskeleton is multi-segmented. Each of the 10 segments is comprised of a ring of a hard material called chitin. The segments are linked by flexible tissues, allowing the abdomen to bend, a necessity for copulation and egg-laying.

Reproductive organs

The genitalia are at the tip of the abdomen. Each species has uniquely shaped genital armature – the male “key” only fitting the correct female “lock”. Because the armature is unique to each species, taxonomists have traditionally relied heavily on microscopic examination of genitalia to determine species and their relationship with other taxa. The advent of DNA analysis and advances in phylogenetics however now mean that genitalia study is just one of many techniques adopted.

Females are equipped with an ovipositor, used to release and deposit the fertilised eggs. In most species this is short and not normally visible, but in certain moths it is modified into a long “sting-like” tube so that the eggs can be inserted into chinks in the bark of trees.

Coremata

The males of many neotropical Arctiid moths, including Creatonotos transiens possess at the tips of their abdomens an extraordinary eversible organ called a coremata. An unmated female “call” to males by releasing pheromones from the tip of her abdomen. Males are attracted by the scent and arrive on the scene, forming a lek, often comprising of a dozen or more individuals.

Experiments have demonstrated that males which have accumulated plant-derived pyrrolizidine alkaloids ( PAs ) then respond by everting their coremata and releasing pheromones. The PAs are passed to females in a spermatophore during copulation, conferring them with toxic qualities that protect them from predation, and also increasing their longevity and fecundity.

Captive males that have been deprived of PAs do not evert their coremata or release pheromones. It seems likely therefore that the females are able to select which males to mate with on the basis of the strength of their pheromones – i.e. choosing the male with the highest PA delivering ability.

Spiracles

On the sides of each segment are microscopic holes called spiracles, through which air enters and leaves the body. Slight rhythmic movements of the body, coordinated with the opening and closing of the spiracles, causes air to be drawn into tiny lung-like sacs, and later expelled.

Digestive system

Butterflies feed exclusively on liquids which may according to species include nectar, dissolved pollen, mineralised water, liquefied dung, urine, sweat, bodily fluids from decomposing animal corpses, and in some cases even tears from the eyes of alligators ! After digestion and extraction of proteins and other minerals the waste matter is expelled from the anus either in liquid form, or as tiny faecal pellets.

Sound producing organs

Insects such as cicadas and grasshoppers are well known for producing courtship songs, but most people only associate other insects with “incidental” sounds such as the buzzing of wings. There is a great deal of evidence however that insects in general, including lepidoptera, produce sounds that fulfil a variety of functions. Many of these sounds are beyond the range of human hearing, and can only be detected with specialised acoustical equipment. In some butterflies however the sounds are clearly audible.

Hamadryas butterflies can produce a crackling sound by twanging 2 tiny prongs on the tip of their abdomens against bristles on the valvae. This is discussed further on the next page.

Nocturnal moths are commonly preyed upon by bats, which project a series of ultrasound clicks and listen to their echoes in order to locate flying moths. Many moths have developed “ears” on their wings or thorax which can alert them to approaching bats, enabling them to take evasive action. The neotropical tiger moth Bertholdia trigona goes a stage further – it actively jams the bats “radar” by producing its own ultrasound, by vibrating a tympanal organ located on its metathorax.

Butterflies and most other adult insects have a pair of spherical compound eyes, each comprising of up to 17000 “ommatidia” – individual light receptors with their own microscopic lenses. These work in unison to produce a mosaic view of the scene around them.

Structure

Each ommatidium consists of a cornea and cone, which together function as a lens. Emerging from the back of each cone is a rod down which light travels to reach a cluster of 2-6 sensory cells, each of which is sensitive to a particular part of the visual spectrum.

The eyes of Skippers are different from those of other butterflies. They have a space between the cones and rods which allows light from each ommatidium to spill into neighbouring rods, effectively increasing their resolution and sensitivity. As a result Skippers can fly very accurately from one spot to another. This different type of eye structure is one of the reasons why taxonomists place them in a different super-family to all other butterflies – the Hesperioidea.

Capabilities

The laws of optics show that it’s likely that everything from about one centimetre to 200 metres will be rendered in sharp focus by butterflies, as their ommatidia are of very short focal length.

The butterfly’s brain can instantly detect whether the image formed by each ommatidium is dark or light. If a predator approaches or if the butterfly moves its head a tiny fraction, the amount of light hitting each receptor changes instantly because of it’s very narrow angle of view. This sensitivity to changes in its surroundings means that a butterfly is extremely efficient at detecting movement and at gauging the distance of an approaching predator, enabling it to take immediate evasive action.

The sensitivity to changes in their visual field, combined with a high flicker-vision frequency of about 150 images per second, may also help butterflies to piece together the thousands of elements of the mosaic image produced by the compound eye. It is not known whether butterflies and other insects are able to merge these mosaic elements into a single image. If are able to do so, it would render them capable of distinguishing patterns at close distances.

Vertebrates need to move their eyes and heads to scan their surroundings, but the compound eyes of butterflies provide them with almost 360 degree vision. They can see everything at the same time, so they can accurately probe into flowers in front of them, and at the same time devote equal concentration to detecting threats from behind.

Butterflies can see polarized light, enabling them to determine the position of the sun, even when it is partly hidden by cloud. This lets them relate their position to the sun and use it as a compass when moving around their habitats.

Colour perception

Humans and birds perceive colours in a different way to butterflies, as the latter are ultra-sensitive to UV as well as visible radiation. Flowers have ultra-violet patterns that are invisible to humans but which can be recognised by butterflies. These UV patterns guide butterflies to the source of nectar in much the same way that runway lights guide an aircraft in to land.

Experiments on Colias butterflies dyed orange, red, green, blue and black have shown that females don’t discriminate between males of different colours. Most biologists agree that visible colours and patterns are NOT used for butterfly-to-butterfly communication. Their primary function is to convey survival-related signals to birds ( i.e. camouflage, aposematic colour, mimetic patterns etc ).

Butterflies can communicate with each-other visually, but they use a “private channel” of ultraviolet patterns which are overlaid on the visible patterns, and cannot be seen by vertebrates. They enable butterflies to recognise conspecifics during the initial “approach” phase of mate location. It has been proven by experimentation that males which have had their UV-reflecting patterns obliterated suffer a significant drop in mate-location success.

As well as being sensitive to UV patterns, butterflies are also alert to the iridescent colours produced when sunlight refracts from the wings of other butterflies. Many species have also evolved selective colour response, i.e. they are “tuned” to react to colours that are dominant in the wing patterns of their own species. Examples include Heliconius erato which is sensitive to red, Morpho helenor which reacts very strongly to blue, and Philaethria dido which is responsive to green.

Shape perception

Male butterflies will intercept and chase any insect of approximately the same size and colour as the female of their own species during the approach phase of mate-location. Experiments using dummy cardboard females have however shown that males respond equally to square, circular, triangular, or butterfly-shaped dummies.

Females of some species however seem capable of recognising plants purely on the basis of leaf-shape and colour. This ability varies from one species to another, and is most highly developed in monophagous butterflies – those whose larvae will only eat one type of plant.

Polyphagous butterflies ( those which utilise several families or genera of larval foodplant ) tend to rely almost exclusively on chemical cues. I have e.g. often observed Pieris napi females searching for oviposition sites. They alight momentarily on various plants, sampling each by puncturing the leaf cuticle with spurs on the legs, to release chemicals in the leaf which are then tasted using the olfactory receptors in the feet. Leaves which were tested included bracken, ivy and oak leaves, all of which are very different in shape from the crucifers needed for oviposition. This appears to indicate that in this species sight plays little or no role in selecting plants for egg-laying.

Vision in nocturnal moths

Elephant Hawkmoths Deilephila elpenor have been studied to determine whether or not nocturnal moths can perceive colour. It seemed unlikely, but Kelber et al found that this species has 9 light receptors in each ommatidium ( compared to between 2-6 in butterflies ); and used behavioural experiments to prove that the moths can discriminate coloured stimuli at intensities corresponding to dim starlight.

Optical maintenance

Insects are unable to blink, so need other ways to protect their eyes. In many butterflies and moths the eyes are shielded by the labial palpi, which act as dust filters. Butterflies in the Satyrine genus Lethe have a dense layer of fine setae or “hairs” on their compound eyes. Studies by the author of these butterflies in Sri Lanka and Borneo indicate that they are strongly attracted to wet dung, and spend long periods probing into it.

It seems plausible therefore that the setae could function in the same way as a cat’s whiskers, acting as tactile sensors that warn them when their eyes get too close to the dung, which would blind them if it stuck to the eye surface.

Antennae

From between the eyes emerge a pair of segmented antennae. These can be voluntarily angled at various positions, and are best thought of as a form of radar. They have many functions including  pheromone detection, which is used for mate location and recognition.

Essex Skipper Thymelicus lineola ( England ) frontal view of antennae – Adrian Hoskins

The antennae of Monarchs Danaus plexippus are covered in over 16000 olfactory ( scent detecting ) sensors – some scale-like, others in the form of hairs or olfactory pits. The scale-like sensors, which number about 13700 in total, are sensitive to sexual pheromones, and to the honey odour which enables them to locate sources of nectar.

Butterfly antennae, like those of ants and bees may also used to communicate physically – e.g. it is common to see male Small Tortoiseshells Aglais urticae drumming their antennae on the hindwings of females during courtship, possibly to “taste” pheromones on the female’s wings. Similar activity can be found in Wood Whites Leptidea sinapis and many other species.

Butterflies are often observed “antenna dipping” – dabbing the antennal tips onto soil or leaves. In this case they are sampling the substrate to detect it’s chemical qualities. They do this to establish whether soil contains essential nutrients. Male butterflies often drink mineralised moisture to obtain sodium, which they pass to the females during copulation.

Differences between butterfly and moth antennae

Butterfly antennae are always clubbed at the tips. In most butterfly subfamilies e.g. Nymphalinae, Heliconiinae and Pierinae the shaft is straight and the club very pronounced, but in the Ithomiinae the antennae thicken progressively towards the tip. The clubs of Skippers ( Hesperiidae ) taper to a fine point and are hooked at the tip, but most other butterflies have rounded ends to the clubs.

Some moths including Burnets ( Zygaenidae ) and Cane Borers ( Castniidae ) also have antennae that are clubbed just like those of butterflies. This is one of many reasons why the “convenience” division of Lepidoptera into butterflies and moths is difficult to justify scientifically.

6-spot Burnet Zygaena filipendulae ( Zygaenidae ), England.

Burnet moths have antennae that are clubbed even more than those of true butterflies – Adrian Hoskins

Male moths from the Saturniidae, Lasiocampidae and a few other families have plumed “pectinate” antennae which are covered in tens of thousands of olfactory sensors, and can detect the scent of females from distances of up to 2km away. The females have no need to detect pheromones, so their antennae, although similar in structure, have very much shorter plumes.

Antenna of male American Oak Silkmoth Antheraea polyphemus – Emily Halsey

Johnston’s organ

At the base of the antennae is a “Johnston’s organ”. This is covered in nerve cells called scolopidia, which are sensitive to stretch, and are used to detect the position of the antennae, as affected by gravity and wind. Thus they are used to sense orientation and balance during flight, and enable the butterflies to finely adjust their direction or rate of ascent / descent. It is also thought possible that they are able to detect magnetic fields when migrating.

Palpi

Protruding from the front of the head are a pair of small projections called labial palpi, which are covered in olfactory ( scent detecting ) sensors. Similar sensors are also located on the antennae, thorax, abdomen and legs.

These sensors are present in a variety of forms, and it is likely that each type fulfils a different role. Sensors on the antennae for example might be “tuned” to locate sexual pheromones, while those on the legs may be sensitive to chemicals exuded by larval foodplants. Logic would indicate that those on the labial palpi and proboscis, due to their position, might be tuned to detect adult food sources such as nectar, urine, carrion or tree sap.

Alternatively it is possible that they might function to detect the “smell” of air which emanates from particular locations – incoming dry desert air for example might be detected and act as a trigger to stimulate migration.

Some biologists argue that in addition to their olfactory functions, palpi have other functions such as shielding the proboscis. Logically this would mean a short proboscis would be associated with small palpi, and a long proboscis associated with larger palpi. In fact this is not the case – species with very long proboscises, such as Saliana skippers and Eurybia Underleafs have average sized palpi, while Libythea Beaks and other species with prominent palpi have unremarkable proboscises.

Another theory is that the palpi may serve as dust filters to protect the surface of the eyes. DeVries states that the most well developed palpi are found in butterflies which feed as adults on rotting fruit or dung where there is a greater probability of soiling the eyes or becoming infested with mites. This theory however doesn’t hold true for Libythea Beak butterflies which have extremely long palpi but which feed at flowers, or in the case of males at mineralised moisture at the edge of puddles.

Beak butterfly Libythea myrrha, showing labial palpi projecting from head – Adrian Hoskins

Proboscis

The proboscis consists of a pair of interlocking c-section channels that when linked together form a tube, much like a drinking straw. This tube can be coiled up like a spring for storage, or extended to enable the butterfly to reach deep into flowers to suck up nectar. If the proboscis gets clogged with sticky fluids the 2 sections can be uncoupled and cleaned.

Olfactory sensors near the tip of the proboscis and in the food canal, together with similar sensors on the tarsus and tibia of the legs, enable butterflies to “taste” nectar, pollen, dung and minerals.

“BD” butterfly Callicore cynosura, using its proboscis as a drinking straw to imbibe dissolved minerals from the surface of a damp rock on the shore of an Amazonian tributary – Adrian Hoskins

Feeding behaviour

In temperate zones most butterflies obtain their sustenance by sucking nectar from flowers. There are exceptions however – male Purple Emperors Apatura iris for example never visits flowers; they feed entirely on fluids which they obtain from sources including dung, carrion, urine-soaked ground, tree sap and honeydew ( aphid secretions ).

In the Alps and Pyrenees mountain ranges of Europe males of many species, particularly Lysandra, Pyrgus, Thymelicus, Cupido & Mellicta often aggregate in groups of several dozen ( and sometimes several hundred ) to imbibe mineralised moisture from the edges of puddles, urine-soaked ground or cattle dung.

This phenomenon is common in alpine regions throughout the northern hemisphere. In the tropics the majority of males from all families follow the behaviour described above for the Purple Emperor. 

Females of some species appear not to feed at all, and rely on proteins and amino acids transferred via the sperm of males during copulation. In the case of Papilionidae, Pieridae and Lycaenidae however females commonly obtain sustenance from flower nectar. In Central & South America female Heliconius butterflies visit Lantana and various other flowers for nectar.

They also 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. The butterflies have acquired the ability to learn and remember the locations of individual pollen plants. They visit these every day, following a predefined circuit through the forest.

Phoebis argante and Rhabdodryas trite aggregating to imbibe moisture, Peru – Adrian Hoskins

Swarms of butterflies, such as males of Eurema, Phoebis, Marpesia, Adelpha, and Callicore, habitually aggregate on river beaches to filter-feed, drinking mineralized water from damp sand. Numerous other species, such as Doxocopa, Rhetus, and Caria, also gather in lesser numbers in similar situations.

Males from subfamilies such as Charaxinae and Apaturinae are commonly attracted to dung, rotting fruit, or carrion. DeVries has estimated that at least 40 percent of all Nymphalidae in Costa Rica feed exclusively on rotting fruit.

The carrion feeders vary enormously in their choice of foodstuff. In Ecuador, I have commonly seen Glasswings feeding on the decomposing corpses of robber flies, and in Venezuela, I watched a male Rhetus periander sucking fluids from the corpse of a giant tarantula. At Pululuhua Crater in Ecuador, I once found scores of high-altitude Satyrines including Lymanopoda, Lasiophila, and Junea feeding on a snake corpse; and at Maquipucuna Cloudforest, I stumbled upon a stunning Necyria avidly feeding on the corpse of a bullfrog.

In temperate regions, carrion-feeding is far less common than in the tropics, but I fondly remember finding six male Purple Emperors (Apatura iris) feeding at the carcass of a deer that was floating in an open cesspit in a thicket in southern England. The butterflies were so stupefied by their unsavory meal that two of them remained on the carcass as I lassoed a rope around the antlers and hauled it to the edge of the cesspit to take photographs!

In the rainforests of South America, many butterflies form associations with ant-bird colonies. The birds follow armies of marauding soldier ants, feeding on insects that scatter as the ants approach. In turn, the butterflies follow the ant-birds, feeding on their liquefied droppings. Biologists studying butterflies in rainforests commonly place tiny wads of dampened white tissue, designed to simulate bird droppings, on leaves to attract butterflies from the families Hesperiinae and Ithomiinae.

The feeding behaviour of butterflies is discussed in greater detail in the individual species accounts, which can be accessed from the galleries or the Species Index.