Lepidoptera (Butterfly / Moth) Temporal range: Early Jurassic-Recent, 190–0 Ma PreЄ Є O S D C P T J K Pg N
Monarch butterfly, Danaus plexippus
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Subclass:	Pterygota
Infraclass:	Neoptera
Superorder:	Endopterygota
Order:	Lepidoptera Linnaeus, 1758
Suborders
Aglossata Glossata Heterobathmiina Zeugloptera

Lepidoptera ( /ˌlɛpɨˈdɒptərə/ lep-i-DOP-tər-ə) is a large order of insects that includes moths and butterflies (called lepidopterans). It is one of the most widespread and widely recognizable insect orders in the world,^[1] encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies. The term was coined by Linnaeus in 1735 and is derived from Ancient Greek λεπίδος (scale) and πτερόν (wing).^[2] Comprising an estimated 174,250 species,^[3] in 126 families^[4] and 46 superfamilies,^[3] the Lepidoptera show many variations of the basic body structure that have evolved to gain advantages in lifestyle and distribution. Recent estimates suggest that the order may have more species than earlier thought,^[5] and is among the four most speciose orders, along with the Hymenoptera, Diptera, and the Coleoptera.^[1]

Lepidopteran species are characterized by more than three derived features, some of the most apparent being the scales covering their bodies and wings, and a proboscis. The scales are modified, flattened "hairs", and give butterflies and moths their extraordinary variety of colors and patterns. Almost all species have some form of membranous wings, except for a few that have reduced wings or are wingless. Like most other insects, butterflies and moths are holometabolous, meaning they undergo complete metamorphosis. Mating and the laying of eggs are carried out by adults, normally near or on host plants for the larvae. The larvae are commonly called caterpillars, and are completely different from their adult moth or butterfly form, having a cylindrical body with a well-developed head, mandible mouth parts, and from 0 to 11 (usually 8) pairs of prolegs. As they grow, these larvae will change in appearance, going through a series of stages called instars. Once fully matured, the larva develops into a pupa, referred to as a chrysalis in the case of butterflies. A few butterflies and many moth species spin a silk case or cocoon prior to pupating, while others do not, instead going underground.^[1]

The Lepidoptera have, over millions of years, evolved a wide range of wing patterns and coloration ranging from drab moths akin to the related order Trichoptera, to the brightly colored and complex-patterned butterflies.^[4] Accordingly, this is the most recognized and popular of insect orders with many people involved in the observation, study, collection, rearing of and commerce in these insects. A person who collects or studies this order is referred to as a lepidopterist.

Butterflies and moths play an important role in the natural ecosystem as pollinators and as food in the food chain; conversely, their larva are considered very problematic to vegetation in agriculture, as their main source of food is often live plant matter. In many species, the female may produce anywhere from 200 to 600 eggs, while in others the number may go as high as 30,000 eggs in one day. The caterpillars hatching from these eggs can cause damage to large quantities of crops. Many moth and butterfly species are of economic interest by virtue of their role as pollinators, the silk they produce or as pest species.

Etymology[link]

The word Lepidoptera comes from the Latin word for "scaly wing", from the Ancient Greek λεπίς (lepis) meaning scale and πτερόν (pteron) meaning wing.^[2] Sometimes the term Rhopalocera is used to group the species that are butterflies, derived from the Ancient Greek ῥόπαλον (rhopalon)^[6]:4150 and κέρας (kæras)^[6]:3993 meaning "club" and "horn", respectively; coming from the shape of the antennae of butterflies.

The origins of the common names "butterfly"and "moth" are varied and often obscure. The English word butterfly is from Old English buttorfleoge, with many variations in spelling. Other than that, the origin is unknown, although it could be derived from the pale yellow color of many species' wings suggesting the color of butter.^[7][8] The species of Heterocera are commonly called moths. The origins of the English word moth are more clear, deriving from the Old English moððe" (cf. Northumbrian dialect mohðe) from Common Germanic (compare Old Norse motti, Dutch mot and German Motte all meaning "moth"). Perhaps its origins are related to Old English maða meaning "maggot" or from the root of "midge", which until the 16th century was used mostly to indicate the larva, usually in reference to devouring clothes.^[9]

The etymological origins of the word "caterpillar", the larval form of butterflies and moths, are from the early 16th century, from Middle English catirpel, catirpeller, probably an alteration of Old North French catepelose: cate, cat (from Latin cattus) + pelose, hairy (from Latin pilōsus).^[10]

Distribution and diversity[link]

Lepidoptera are among the most successful groups of insects. They are found on all continents, except Antarctica. Lepidoptera inhabit all terrestrial habitats ranging from desert to rainforest, from lowland grasslands to montane plateaus but almost always associated with higher plants, especially angiosperms (flowering plants).^[11] Among the most northern dwelling species of butterflies and moths is the Arctic Apollo (Parnassius arcticus), which is found in the Arctic Circle in northeastern Yakutia, at an altitude of 1500 meters above sea level.^[12] In the Himalayas, various Apollo species such as Parnassius epaphus, besides others, have been recorded to occur up to an altitude of 6,000 meters above sea level.^[13]:221

Some lepidopteran species exhibit symbiotic, phoretic, or parasitic life-styles, inhabiting the bodies of organisms rather than the environment. Coprophagous pyralid moth species, called sloth moths, such as Bradipodicola hahneli and Cryptoses choloepi, are unusual in that they are exclusively found inhabiting the fur of sloths, mammals found in Central and South America.^[14][15] Two species of Tinea moths have been recorded as feeding on horny tissue and have been bred from the horns of cattle. The larva of Zenodochium coccivorella is an internal parasite of the coccid Kermes species. Many species have been recorded as breeding in natural materials or refuse such as owl pellets, bat caves, honey-combs or diseased fruit.^[15]

Of the approximately 174,250 lepidopteran species described until 2007, butterflies and skippers are estimated to comprise approximately 17,950, with moths making up the rest.^[3][16] The vast majority of Lepidoptera are to be found in the tropics, but substantial diversity exists on most continents. North America has over 700 species of butterflies and over 11,000 species of moths,^[17][18] while there are about 400 species of butterflies and 14,000 species of moths reported from Australia.^[19] The diversity of Lepidoptera in each faunal region has been estimated by John Heppner in 1991 based partly on actual counts from the literature, partly on the card indices in the Natural History Museum (London) and the National Museum of Natural History (Washington), and partly on estimates:^[5]:726

External morphology[link]

Parts of an adult butterfly

A – head, B – thorax, C – abdomen, 1 – prothoracic shield, 2 – spiracle, 3 – true legs, 4 – midabdominal prolegs, 5 – anal proleg, 6 – anal plate, 7 – tentacle, a – frontal triangle, b – stemmata (ocelli), c – antenna, d – mandible, e – labrum.

Lepidoptera are morphologically distinguished from other orders principally by the presence of scales on the external parts of the body and appendages, especially the wings. Butterflies and moths vary in size from microlepidoptera only a few millimeters long, to conspicuous animals with a wingspan of many inches, such as the Monarch butterfly and Atlas moth.^[20]:246 Lepidopterans undergo a four-stage life cycle: egg; larva or caterpillar; pupa or chrysalis; and imago (plural: imagines) / adult and show many variations of the basic body structure, which have evolved to gain advantages in lifestyle and distribution.

Head[link]

The face of a caterpillar with the mouthparts showing

The head is where many sensing organs and the mouth parts are found. Like the adult, the larva also have a toughened, or sclerotized head capsule.^[21] Here, there are two compound eyes, and chaetosema, raised spots or clusters of sensory bristles unique to Lepidoptera, even though many taxa have lost one or both of these spots. The antennae have a wide variation in form among species and even between different sexes. The antennae of butterflies are usually filiform and shaped like clubs, those of the skippers are hooked while those of moths have flagellar segments variously enlarged or branched. Some moths have antennae that are enlarged, or tapered and hooked at the ends.^[22]:559-560

The maxillary galeae are modified and form an elongated proboscis. The proboscis consists of one to five segments, usually kept coiled up under the head by small muscles when it is not being used to suck up nectar from flowers or other liquids. Some basal moths still have mandibles, or separate moving jaws, like their ancestors and these form the family Micropterigidae.^{[21][22]:560[23]}

The larvae, called caterpillars, have a toughened head capsule. Caterpillars lack the proboscis and have separate chewing mouthparts.^[21] These mouthparts, called mandibles, are used to chew up the plant matter that the larvae eat. The lower jaw, or labium, is weak but may carry a spinneret, an organ used to create silk. The head is made of large lateral lobes, each having an ellipse of up to six simple eyes.^[22]:562-563

Thorax[link]

The thorax is made of three fused segments, the prothorax, mesothorax, and metathorax, each with a pair of legs. The first segment contains the first pair of legs. In some males of the butterfly family Nymphalidae, the fore-legs are greatly reduced and are not used for walking or perching.^[22]:586 The three pairs of legs are covered with scales. Lepidoptera also have olfactory organs on their feet, which aid the butterfly in "tasting" or "smelling" out its food.^[24] In the larval form there are 3 pairs of true legs, with 0–11 pairs of abdominal legs (usually 8) and hooklets, called apical crochets.^[11]

The two pairs of wings are found on the middle and third segment, or mesothorax and metathorax respectively. In the more recent genera, the wings of the second segment are much more pronounced, although some more primitive forms have similarly sized wings of both segments. The wings are covered in scales arranged like shingles, which form an extraordinary variety of colors and patterns. The mesothorax is designed to have more powerful muscles to propel the moth or butterfly through the air, with the wing of this segment (forewing) having a stronger vein structure.^[22]:560 The largest superfamily, Noctuidae, have the wings modified to act as Tympanal or hearing organs^[25]

The caterpillar has an elongated soft body that may have hair-like or other projections, 3 pairs of true legs, with 0–11 pairs of abdominal legs (usually 8) and hooklets, called apical crochets.^[11] The thorax will usually have a pair of legs on each segment. The thorax is also lined with many spiracles on both the mesothorax and metathorax, except for a few aquatic species, who instead have a form of gill.^[22]:563

Abdomen[link]

The abdomen, which is less sclerotized than the thorax, consists of 10 segments with membranes in between allowing for articulated movement. The sternum, on the first segment, is small in some families and is completely absent in others. The last 2 or 3 segments form the external parts of the species' sex organs. The genitalia of Lepidoptera are highly varied and are often the only means of differentiating between species. Male genitals include a valva, which is usually large, as it is used to grasp the female during mating. Female genitalia include three distinct sections.

In the females of basal moths, there is only one sex organ, which is used for copulation and as a ovipositor, or egg laying organ. 98% of moth species have a separate organ for mating, and an external duct that carries the sperm from the male.^[22]:561

The abdomen of the caterpillar has 4 pairs of prolegs, normally located on the third to sixth segments of the abdomen, and a separate pair of prolegs by the anus, which have a pair of tiny hooks called crotchets. These aid in gripping and walking, especially in species that lack many prolegs (e. g. larvae of Geometridae). In some basal moths, these prolegs may be on every segment of the body, while prolegs may be lost completely in other groups, which are more adapted to boring and living in sand (e. g., Prodoxidae and Nepticulidae respectively).^[22]:563

Scales[link]

Wing scales form the color and pattern on wings. The scales shown here are lamellar. The pedicel can be seen attached to a few loose scales.

The wings, head parts of thorax and abdomen of Lepidoptera are covered with minute scales, from which feature the order 'Lepidoptera' derives its names, the word "lepteron" in Ancient Greek meaning 'scale'. Most scales are lamellar, or blade-like and attached with a pedicel, while other forms may be hair-like or specialized as secondary sexual characteristics.^[26] The lumen or surface of the lamella, has a complex structure. It gives color either due to the pigmentary colors contained within or due to its three-dimensional structure.^[27] Scales provide a number of functions, which include insulation, thermoregulation, aiding gliding flight, among others, the most important of which is the large diversity of vivid or indistinct patterns they provide, which help the organism protect itself by camouflage, mimicry, and to seek mates.^[26]

Electron microscopic images of scales

A patch of wing (×50)

Scales close up (×200)

A single scale (×1000)

Microstructure of a scale (×5000)

Internal morphology[link]

In the reproductive system of butterflies and moths, the male genitalia are complex and unclear. In females there are three types of genitalia based on the relating taxa: monotrysian, exoporian, and ditrysian. In the monotrysian type there is an opening on the fused segments of the sterna 9 and 10, which act as insemination and oviposition. In the exoporian type (in Hepaloidae and Mnesarchaeoidea) there are two separate places for insemination and oviposition, both occurring on the same sterna as the monotrysian type, i.e. 9 and 10.^[20] The ditrysian groups have an internal duct that carry sperm, with separate openings for copulation and egg-laying^[1] In most species the genitalia are flanked by two soft lobes, although they may be specialized and sclerotized in some species for ovipositing in area such as crevices and inside plant tissue.^[20] Hormones and the glands that produce them run the development of butterflies and moths as they go through their life cycle, called the endocrine system. The first insect hormone PTTH (Prothoracicotropic hormone) operates the species life cycle and diapause (see the relates section).^[28] This hormone is produced by corpora allata and corpora cardiaca, where it is also stored. Some glands are specialized to perform certain task such as producing silk or producing saliva in the palpi.^{[29]:65, 75} While the corpora cardiaca produce PTTH, the corpora allata also produces jeuvanile hormones, and the prothorocic glands produce moulting hormones.

In the digestive system, the anterior region of the foregut has been modified to form a pharyngeal sucking pump as they need it for the food they eat, which are for the most part liquids. An esophagus follows and leads to the posterior of the pharynx and in some species forms a form of crop. The midgut is short and straight, with the hindgut being longer and coiled.^[20] Ancestors of lepidopteran species, stemming from Hymenoptera, had midgut ceca, although this is lost in current butterflies and moths. Instead, all the digestive enzymes other than initial digestion, are immobilized at the surface of the midgut cells. In larvae, long-necked and stalked goblet cells are found in the anterior and posterior midgut regions, respectively. In insects, the goblet cells excrete positive potassium ions, which are absorbed from leaves ingested by the larvae. Most butterflies and moths display the usual digestive cycle, however species that have a different diet require adaptations to meet these new demands.^[22]:279

Internal morphology of adult male in the family Nymphalidae, showing most of the major organ systems, with characteristic reduced forelegs of that family. The corpora include the corpus allatum and the corpus cardiaca.

In the circulatory system, hemolymph, or insect blood, is used to circulate heat in a form of thermoregulation, where muscles contraction produces heat, which is transferred to the rest of the body when conditions are unfavorable.^[30] In lepidopteran species, hemolymph is circulated through the veins in the wings by some form of pulsating organ, either by the heart or by the intake of air into the trachea.^[29]:69 Air is taken in through spiracles along the sides of the abdomen and thorax supplying the trachea with oxygen as it goes through the lepidopteran's respiratory system. There are three different tracheae supplying oxygen diffusing oxygen throughout the species body: The dorsal, ventral, and visceral. The dorsal tracheae supply oxygen to the dorsal musculature and vessels, while the ventral tracheae supply the ventral musculature and nerve cord, and the visceral tracheae supply the guts, fat bodies, and gonads.^{[29]:71, 72}

Polymorphism[link]

Sexually dimorphic bagworm moths (Thyridopteryx ephemeraeformis) mating. The female is flightless.

The Heliconius butterflies from the tropics of the Western Hemisphere are the classical model for Müllerian mimicry.

Polymorphism is the appearance of forms or "morphs", which differ in color and number of attributes within a single species.^[11]:163[31] In Lepidoptera, polymorphism can be seen not only between individuals in a population, but also between the sexes as sexual dimorphism, between geographically separated populations in geographical polymorphism and also between generations flying at different seasons of the year (seasonal polymorphism or polyphenism). In some species, the polymorphism is limited to one sex, typically the female. This often includes the phenomenon of mimicry when mimetic morphs fly alongside non-mimetic morphs in a population of a particular species. Polymorphism occurs both at specific level with heritable variation in the overall morphological design of individuals as well as in certain specific morphological or physiological traits within a species.^[11]

Environmental polymorphism, in which traits are not inherited, is often termed as polyphenism. Polyphenism in Lepidoptera is commonly seen in the form of seasonal morphs especially in the butterfly families of Nymphalidae and Pieridae. An Old World pierid butterfly, the Common Grass Yellow (Eurema hecabe) has a darker summer adult morph, triggered by a long day exceeding 13 hours in duration, while the shorter diurnal period of 12 hours or less induces a paler morph in the post-monsoon period.^[32] Polyphenism also occurs in caterpillars, an example being the Peppered Moth, Biston betularia.^[33]