General description Butterfly adults are characterised by their four
scale-covered wings, which give the Lepidoptera their name (
Ancient Greek λεπίς lepís, scale + πτερόν pterón, wing). These scales give butterfly wings their colour; they are pigmented with
melanins that give them blacks and browns, as well as
uric acid derivatives and
flavones that give them yellows, but many of the blues, greens, reds and
iridescent colours are created by
structural coloration produced by the micro-structures of the scales and hairs. As in all insects, the body is divided into three sections: the head,
thorax, and
abdomen. The thorax is composed of three segments, each with a pair of legs. In most families of butterfly the antennae are clubbed (clavate), unlike those of
moths which may be threadlike (filiform) or feathery (plumose). The long proboscis can be coiled when not in use for sipping nectar from flowers. File:Inachis io top detail MichaD crop.jpg|A zoomed in view of the wing scales on a
Aglais io, or peacock butterfly. File:Arctia caja Buchstein02.jpg|Most butterflies fly by day, most moths by night: but
Arctia caja is day-flying. File:antennae ctb.png|Butterfly antennal shapes, mainly clubbed, unlike those of moths. Drawn by C. T. Bingham, 1905 Nearly all butterflies are
diurnal, have relatively bright colours, and hold their wings vertically above their bodies when at rest; these features differentiate butterflies from the majority of moths, which fly by night, are often
cryptically coloured (well camouflaged), and either hold their wings flat (touching the surface on which the moth is standing) or fold them closely over their bodies. Some day-flying moths, such as the
hummingbird hawk-moth, are exceptions to these rules. Butterfly
larvae,
caterpillars, have a hard (
sclerotised) head with strong mandibles used for cutting their food, most often leaves. They have cylindrical bodies, with ten segments to the abdomen, generally with short prolegs on segments 3–6 and 10; the three pairs of true legs on the thorax have five segments each.
Distribution and migration Butterflies are distributed worldwide except Antarctica, totalling some 18,500 species. The
monarch butterfly is native to the Americas, but in the nineteenth century or before, spread across the world, and is now found in Australia, New Zealand, other parts of Oceania, and the
Iberian Peninsula. It is not clear how it dispersed; adults may have been blown by the wind or larvae or pupae may have been accidentally transported by humans, but the presence of suitable host plants in their new environment was a necessity for their successful establishment. migration route trees near
Angangueo, Mexico. Many butterflies, such as the
painted lady, monarch, and several
danaine migrate for long distances. These migrations take place over a number of generations and no single individual completes the whole trip. The eastern North American population of monarchs can travel thousands of miles south-west to
overwintering sites in Mexico. There is a reverse migration in the spring. It has recently been shown that the British painted lady undertakes a round trip in a series of steps by up to six successive generations, from tropical Africa to the Arctic Circle — almost double the length of the famous migrations undertaken by monarch. Spectacular large-scale migrations associated with the
monsoon are seen in peninsular India. Migrations have been studied in more recent times using wing tags and also using
stable hydrogen isotopes. Butterflies navigate using a time-compensated sun compass. They can see polarised light and therefore orient even in cloudy conditions. The polarised light near the ultraviolet spectrum appears to be particularly important. Many migratory butterflies live in semi-arid areas where breeding seasons are short. The life histories of their host plants also influence butterfly behaviour.
Life cycle Butterflies in their adult stage can live from a week to nearly a year depending on the species. Many species have long larval life stages while others can remain
dormant in their pupal or egg stages and thereby survive winters. The
Melissa Arctic (
Oeneis melissa) overwinters twice as a caterpillar. Butterflies may have one or more broods per year. The number of generations per year varies from
temperate to
tropical regions with tropical regions showing a trend towards
multivoltinism. on
greater pignut '') has
pheromone-releasing "sex brands" (dark line) on the upperside of its forewings.
Courtship is often aerial and often involves
pheromones. Butterflies then land on the ground or on a perch to mate. The male passes a
spermatophore to the female; to reduce sperm competition, he may cover her with his scent, or in some species such as the Apollos (
Parnassius)
plugs her genital opening to prevent her from mating again. The vast majority of butterflies have a four-stage life cycle:
egg,
larva (caterpillar),
pupa (chrysalis) and
imago (adult). In the genera
Colias,
Erebia,
Euchloe, and
Parnassius, a small number of species are known that reproduce
semi-parthenogenetically; when the female dies, a partially developed larva emerges from her abdomen. Butterfly eggs are fixed to a leaf with a special glue which hardens rapidly. As it hardens it contracts, deforming the shape of the egg. This glue is easily seen surrounding the base of every egg forming a meniscus. The nature of the glue has been little researched but in the case of
Pieris brassicae, it begins as a pale yellow granular secretion containing acidophilic proteins. This is viscous and darkens when exposed to air, becoming a water-insoluble, rubbery material which soon sets solid. Butterflies in the genus
Agathymus do not fix their eggs to a leaf; instead, the newly laid eggs fall to the base of the plant. Eggs are almost invariably laid on plants. Each species of butterfly has its own host plant range and while some species of butterfly are restricted to just one species of plant, others use a range of plant species, often including members of a common family. In some species, such as the
great spangled fritillary, the eggs are deposited close to but not on the food plant. This most likely happens when the egg overwinters before hatching and where the host plant loses its leaves in winter, as do
violets in this example. The egg stage lasts a few weeks in most butterflies, but eggs laid close to winter, especially in temperate regions, go through a
diapause (resting) stage, and the hatching may take place only in spring. Some temperate region butterflies, such as the
Camberwell beauty, lay their eggs in the spring and have them hatch in the summer.
Caterpillar larva caterpillar of
Papilio machaon, in threat pose Butterfly larvae, or caterpillars, consume plant leaves and spend practically all of their time searching for and eating food. Although most caterpillars are herbivorous, a few species are
predators:
Spalgis epius eats
scale insects, while lycaenids such as
Liphyra brassolis are
myrmecophilous, eating ant larvae. : ant tending a
lycaenid caterpillar,
Catapaecilma major Some larvae, especially those of the
Lycaenidae, form
mutual associations with ants. They communicate with the ants using vibrations that are transmitted through the
substrate as well as using chemical signals. The ants provide some degree of protection to these larvae and they in turn gather
honeydew secretions.
Large blue (
Phengaris arion) caterpillars trick
Myrmica ants into taking them back to the
ant colony where they feed on the ant eggs and larvae in a parasitic relationship.
countershaded caterpillar of a hawkmoth,
Ceratomia amyntor Caterpillars mature through a series of developmental stages known as
instars. Near the end of each stage, the larva undergoes a process called
apolysis, mediated by the release of a series of
neurohormones. During this phase, the
cuticle, a tough outer layer made of a mixture of
chitin and specialised
proteins, is released from the softer
epidermis beneath, and the epidermis begins to form a new cuticle. At the end of each instar, the larva
moults, the old cuticle splits and the new cuticle expands, rapidly hardening and developing pigment. Caterpillars have short antennae and several
simple eyes. The
mouthparts are adapted for chewing with powerful mandibles and a pair of maxillae, each with a segmented palp. Adjoining these is the labium-hypopharynx which houses a tubular spinneret which is able to extrude silk. Butterfly caterpillars have three pairs of true legs on the thoracic segments and up to six pairs of
prolegs arising from the abdominal segments. These prolegs have rings of tiny hooks called crochets that are engaged hydrostatically and help the caterpillar grip the substrate. The epidermis bears tufts of
setae, the position and number of which help in identifying the species. There is also decoration in the form of hairs, wart-like protuberances, horn-like protuberances and spines. Internally, most of the body cavity is taken up by the gut, but there may also be large silk glands, and special glands which secrete distasteful or toxic substances. The developing wings are present in later stage instars and the
gonads start development in the egg stage. The pupal transformation into a butterfly through
metamorphosis has held great appeal to mankind. To transform from the miniature wings visible on the outside of the pupa into large structures usable for flight, the pupal wings undergo rapid mitosis and absorb a great deal of nutrients. If one wing is surgically removed early on, the other three will grow to a larger size. In the pupa, the wing forms a structure that becomes compressed from top to bottom and pleated from proximal to distal ends as it grows, so that it can rapidly be unfolded to its full adult size. Several boundaries seen in the adult colour pattern are marked by changes in the expression of particular transcription factors in the early pupa.
Adult '' butterfly The reproductive stage of the insect is the winged adult or
imago. The surface of both butterflies and moths is covered by scales, each of which is an outgrowth from a single
epidermal cell. The head is small and dominated by the two large
compound eyes. These are capable of distinguishing flower shapes or motion but cannot view distant objects clearly. Colour perception is good, especially in some species in the blue/violet range. The
antennae are composed of many segments and have clubbed tips (unlike moths that have tapering or feathery antennae). The sensory receptors are concentrated in the tips and can detect odours. Taste receptors are located on the palps and on the feet. The mouthparts are adapted to sucking and the
mandibles are usually reduced in size or absent. The first maxillae are elongated into a tubular
proboscis which is curled up at rest and expanded when needed to feed. The first and second maxillae bear palps which function as sensory organs. Some species have a reduced proboscis or maxillary palps and do not feed as adults. in these species only 20% of the amino acids used in reproduction come from larval feeding, which allow them to develop more quickly as caterpillars, and gives them a longer lifespan of several months as adults. The thorax of the butterfly is devoted to locomotion. Each of the three thoracic segments has two legs (among
nymphalids, the first pair is reduced and the insects walk on four legs). The second and third segments of the thorax bear the wings. The leading edges of the forewings have thick veins to strengthen them, and the hindwings are smaller and more rounded and have fewer stiffening veins. The forewings and hindwings are not hooked together (
as they are in moths) but are coordinated by the friction of their overlapping parts. The front two segments have a pair of
spiracles which are used in respiration.
Pattern formation The colourful patterns on many butterfly wings tell potential predators that they are toxic. Hence, the genetic basis of wing
pattern formation can illuminate both the
evolution of butterflies as well as their
developmental biology. The colour of butterfly wings is derived from tiny structures called scales, each of which have their own
pigments. In
Heliconius butterflies, there are three types of scales: yellow/white, black, and red/orange/brown scales. Some mechanism of wing pattern formation are now being investigated using genetic techniques. For instance, a
gene called
cortex determines the colour of scales: deleting
cortex turned black and red scales yellow. Mutations, e.g.
transposon insertions of the
non-coding DNA around the
cortex gene, can turn a black-winged butterfly into a butterfly with a yellow wing band.
Mating When the butterfly
Bicyclus anynana is subjected to repeated inbreeding in the laboratory, there is a dramatic decrease in egg hatching. This severe
inbreeding depression is considered to be likely due to a relatively high
mutation rate to recessive
alleles with substantial damaging effects and infrequent episodes of
inbreeding in nature that might otherwise purge such mutations. During mate selection, adult females do not innately avoid or learn to avoid siblings, implying that such detection may not be critical to reproductive fitness. tree sap, rotting fruit, dung, decaying flesh, and dissolved minerals in wet sand or dirt. Butterflies are important as pollinators for some species of plants. In general, they do not carry as much pollen load as
bees, but they are capable of moving pollen over greater distances.
Flower constancy has been observed for at least one species of butterfly. Adult butterflies consume only liquids, ingested through the proboscis. They sip water from damp patches for hydration and feed on nectar from flowers, from which they obtain sugars for energy, and
sodium and other minerals vital for reproduction. Several species of butterflies need more sodium than that provided by nectar and are attracted by sodium in salt; they sometimes land on people, attracted by the salt in human sweat. Some butterflies also visit dung and scavenge rotting fruit or carcasses to obtain minerals and nutrients. In many species, this
mud-puddling behaviour is restricted to the males, and studies have suggested that the nutrients collected may be provided as a
nuptial gift, along with the spermatophore, during mating. In
hilltopping, males of some species seek hilltops and ridge tops, which they patrol in search for females. Since it usually occurs in species with low population density, it is assumed these landscape points are used as meeting places to find mates. Butterflies use their antennae to sense the air for wind and scents. The antennae come in various shapes and colours; the hesperiids have a pointed angle or hook to the antennae, while most other families show knobbed antennae. The antennae are richly covered with sensory organs known as
sensillae. A butterfly's sense of taste is coordinated by chemoreceptors on the
tarsi, or feet, which work only on contact, and are used to determine whether an egg-laying insect's offspring will be able to feed on a leaf before eggs are laid on it. Many butterflies use chemical signals,
pheromones; some have specialised scent scales (
androconia) or other structures (
coremata or "hair pencils" in the Danaidae). Vision is well developed in butterflies and most species are sensitive to the ultraviolet spectrum. Many species show sexual dimorphism in the patterns of UV reflective patches. Colour vision may be widespread but has been demonstrated in only a few species. Some butterflies have organs of hearing and some species make
stridulatory and clicking sounds. Many species of butterfly maintain territories and actively chase other species or individuals that may stray into them. Some species will bask or perch on chosen perches. The flight styles of butterflies are often characteristic and some species have courtship flight displays. Butterflies can only fly when their temperature is above ; when it is cool, they can position themselves to expose the underside of the wings to the sunlight to heat themselves up. If their body temperature reaches , they can orientate themselves with the folded wings edgewise to the sun. Basking is an activity which is more common in the cooler hours of the morning. Some species have evolved dark wingbases to help in gathering more heat and this is especially evident in alpine forms. As in many other insects, the
lift generated by butterflies is more than can be accounted for by steady-state, non-transitory
aerodynamics. Studies using
Vanessa atalanta in a
wind tunnel show that they use a wide variety of aerodynamic mechanisms to generate force. These include
wake capture,
vortices at the wing edge, rotational mechanisms and the
Weis-Fogh '
clap-and-fling' mechanism. Butterflies are able to change from one mode to another rapidly.
Ecology Parasitoids, predators, and pathogens parasitoidal wasp (
Apanteles species) cocoons attached to lime butterfly (
Papilio demoleus) caterpillar Butterflies are threatened in their early stages by
parasitoids and in all stages by predators, diseases and environmental factors.
Braconid and other parasitic wasps lay their eggs in lepidopteran eggs or larvae and the wasps' parasitoid larvae devour their hosts, usually pupating inside or outside the desiccated husk. Most wasps are very specific about their host species and some have been used as biological controls of pest butterflies like the
large white butterfly. When the
small cabbage white was accidentally introduced to New Zealand, it had no natural enemies. In order to control it, some pupae that had been parasitised by a chalcid wasp were imported, and natural control was thus regained. Some flies lay their eggs on the outside of caterpillars and the newly hatched fly larvae bore their way through the skin and feed in a similar way to the parasitoid wasp larvae. Predators of butterflies include ants, spiders, wasps, and birds. Caterpillars are also affected by a range of bacterial, viral and fungal diseases, and only a small percentage of the butterfly eggs laid ever reach adulthood.
Endangered species Queen Alexandra's birdwing, found in
Papua New Guinea, is the largest butterfly in the world. The species is
endangered, and is one of only three insects (the other two being butterflies as well) to be listed on
Appendix I of
CITES, making international trade illegal.
Defences Butterflies protect themselves from predators by a variety of means. Chemical defences are widespread and are mostly based on chemicals of plant origin. In many cases the plants themselves evolved these toxic substances as
protection against herbivores. Butterflies have evolved mechanisms to sequester these plant toxins and use them instead in their own defence. These defence mechanisms are effective only if they are well advertised; this has led to the evolution of bright colours in unpalatable butterflies (
aposematism). This signal is commonly
mimicked by other butterflies, usually only females. A
Batesian mimic imitates another species to enjoy the protection of that species' aposematism.
Müllerian mimicry occurs when aposematic species evolve to resemble each other, presumably to reduce predator sampling rates;
Heliconius butterflies from the Americas are a good example.
Camouflage is found in many butterflies. Some like the oakleaf butterfly and
autumn leaf are remarkable imitations of leaves. As caterpillars, many defend themselves by freezing and appearing like sticks or branches. Others have
deimatic behaviours, such as rearing up and waving their front ends which are marked with eyespots as if they were snakes. Some papilionid caterpillars such as the giant swallowtail (
Papilio cresphontes) resemble bird droppings so as to be passed over by predators. Some caterpillars have hairs and bristly structures that provide protection while others are gregarious and form dense aggregations. Behavioural defences include perching and angling the wings to reduce shadow and avoid being conspicuous. Some female
Nymphalid butterflies guard their eggs from parasitoidal
wasps. The Lycaenidae have a false head consisting of eyespots and small tails (false antennae) to deflect attack from the more vital head region. These may also cause ambush predators such as spiders to approach from the wrong end, enabling the butterflies to detect attacks promptly. Many butterflies have
eyespots on the wings; these too may deflect attacks, or may serve to attract mates. Auditory defences can also be used, which in the case of the
grizzled skipper refers to vibrations generated by the butterfly upon expanding its wings in an attempt to communicate with ant predators. Many tropical butterflies have
seasonal forms for dry and wet seasons. These are switched by the hormone
ecdysone. The dry-season forms are usually more cryptic, perhaps offering better camouflage when vegetation is scarce. Dark colours in wet-season forms may help to absorb solar radiation. File:Heliconius mimicry.png|
Heliconius warns off predators with
Müllerian mimicry. File:Papilio cresphontes larva defensive.JPG|
Giant swallowtail caterpillar everting its
osmeterium in defence; it is also
mimetic, resembling a bird dropping. File:Bird-damaged Speckled Wood Pararge aegeria.JPG|Eyespots of
speckled wood (
Pararge aegeria) distract predators from attacking the head. This insect can still fly with a damaged left hindwing. ==Declining numbers==