External morphology of Lepidoptera

In common with other members of the superorder Holometabola, Lepidoptera undergo complete metamorphosis, going through a four-stage life cycle: egg, larva / caterpillar, pupa / chrysalis, and imago (plural: imagines) / adult. Lepidopterans range in size from a few millimetres in length, such as in the case of microlepidoptera, to a wingspan of many inches, such as the Atlas moth and the world's largest butterfly Queen Alexandra's birdwing. General body plan The body of an adult butterfly or moth (the imago) has three distinct divisions, called tagmata, connected at constrictions; these tagmata are the head, thorax, and abdomen. Adult lepidopterans have four wings – a forewing and a hindwing on both the left and the right side of the thorax – and, like all insects, three pairs of legs. The morphological characteristics which distinguish the order Lepidoptera from other insect orders are: • the mouthparts • the shape and venation of the wings • whether the wings are homoneurous (the venation of the forewings and hindwings alike) or heteroneurous (forewings and hindwings different) • whether the wings are aculeate (more or less covered with specialized bristles called microsetae) or nonaculeate • the type of wing coupling (jugate or frenate) • the anatomy of the reproductive organs • the structure of larva and position of primary setae • whether the pupa is exarate or obtect The morphological characteristics of caterpillars and pupae used for classification are completely different from that of adults; different classification schemes are sometimes provided separately for classifying adults, larvae, and pupae. The characteristics of immature stages are increasingly used for taxonomic purposes as they provide insights into systematics and phylogenies of Lepidoptera that are not apparent from examination of adults. == Head ==

head illustration from G. F. Hampson's Moths of British India Vol. 1 (1892) Like all animal heads, the head of a butterfly or moth contains the feeding organs and the major sense organs. The head typically consists of two antennae, two compound eyes, two palpi, and a proboscis. The head capsule is well sclerotised and has a number of sclerites or plates, separated by sutures. The sclerites are difficult to distinguish from sulci (singular – sulcus) which are secondary thickenings. The regions of the head have been divided into a number of areas which act as a topographical guide for description by lepidopterists but cannot be discriminated in terms of their development. File:Insect SEM gracilariidae.jpg|Head of a moth of family Gracillariidae showing extent of scales on the head File:Rough-scaled_Lepidoptera_head.jpg|Rough-scaled head of moth Monopis icterogastra (family Tineidae) File:Smooth-scaled_Lepidoptera_head.jpg|Smooth-scaled head of moth Glyphipterix simpliciella (family Glyphipterigidae) File:Smooth-scaled_Lepidoptera_head 2.jpg|Smooth-scaled head of moth Stegasta variana (family Gelechiidae) Antennae Antennae are prominent paired appendages that project forwards between the animal's eyes and consist of a number of segments. In the case of butterflies, their length varies from half the length of the forewing to three-quarters of the length of the forewing. The antennae of butterflies are either slender and knobbed at the tip and, in the case of the Hesperiidae, are hooked at the tip. In some butterfly genera such as Libythea and Taractrocera the knob is hollowed underneath. Some moths have knobbed antennae akin to those of butterflies, such as the family Castniidae. Antennae are the primary organs of olfaction (smell) in Lepidoptera. The antenna surface is covered with large numbers of olfactory scales, hairs, or pits; as many as 1,370,000 are found on the antennae of a monarch. Antennae are extremely sensitive; the feathered antennae of male moths from the Saturniidae, Lasiocampidae, and many other families are so sensitive that they can detect the pheromones of female moths from distances of up to away. Lepidoptera antennae can be angled in many positions. They help the insect in locating the scent and can be considered to act as a kind of "olfactory radar". File:Eriocrania_cicatricella_cropped.jpg| File:Abantiades_barcas_cropped.jpg| File:Actias_artemis_cropped.jpg| File:Silver-spotted_Skipper%2C_Megan_McCarty58_cropped.jpg| File:Vanessa_February_2008-1.jpg| File:Deleiphila_elpenor_003_cropped.JPG| File:CastniidaeMexico.JPG| File:Nemophora_degeerella-01_(xndr).jpg| Eyes ''. of Mythimna unipuncta seen to the right of the base of the antenna, in close contact with the compound eye. Lepidoptera has two large, immovable compound eyes, which consist of a large number of facets or lenses, each connected to a lens-like cylinder that is attached to a nerve leading to the brain. The eyes are usually smooth but may be covered by minute hairs. The eyes of butterflies are usually brown, golden brown, or even red as in the case of some species of skippers. The ocelli are not homologous to the simple eyes of caterpillars which are differently named as stemmata. from which an interesting adaptive departure is the unusually long-tongued sphinx moth Xanthopan morganii praedicta. Charles Darwin predicted the existence and proboscis length of this moth before its discovery based on his knowledge of the long-spurred Madagascan star orchid Angraecum sesquipedale. There are primarily two feeding guilds in Lepidoptera – the nectarivorous who obtain the majority of their nutritional requirements from floral nectar and those of the frugivorous guild who feed primarily on juices of rotting fruit or fermenting tree sap. There are substantial differences between the morphology of the proboscises of both feeding guilds. Hawkmoths (family Sphingidae) have elongated proboscises, which enable them to feed on and pollinate flowers with long tubular corollas. Besides this, some taxa (especially noctuid moths) have evolved different proboscis morphologies. Certain noctuid species have developed piercing mouthparts; the proboscis has sclerotized scales on the tip with which to pierce and suck blood or fruit juices. Proboscises in some Heliconius species have evolved to consume solids such as pollen. Some other moths, mostly noctuids, have modified proboscises to suit their mode of nutrition – lachryphagy (feeding on tears of sleeping birds). The proboscises often have sharp apices and a host of barbs and spurs on the stem. File:Butterfly tongue.jpg|Scanning electron micrograph of the proboscis of a moth from family Pyralidae File:Siproeta stelenes (Green Malachite) sucking a banana.JPG|A nymphalid butterfly sucking on a banana File:Heliconius sara-01 (xndr).jpg|Sara longwing (Heliconius sara), one of many Heliconius species known to feed on pollen, with pollen on its proboscis File:NHM_Xanthopan_morgani.jpg|Xanthopan morganii, an African sphingid, has a foot-long proboscis adapted for feeding from the orchid Angraecum sesquipedale File:A_butterfly_feeding_on_the_tears_of_a_turtle_in_Ecuador.jpg|Lachryphagous Lepidoptera, such as the two Julia butterflies (Dryas iulia) drinking the tears of turtles in Ecuador, have hooks and barbs at the tip of the proboscis == Thorax ==

The thorax, which develops from segments 2, 3, and 4 of the larva, consists of three invisibly divided segments, namely prothorax, metathorax, and mesothorax. The upper and lower parts of the thorax (terga and sterna respectively) are composed of segmental and intrasegmental sclerites which display secondary sclerotisation and considerable modification in the Lepidoptera. The prothorax is the simplest and smallest of the three segments while the mesothorax is the most developed. In Lepidoptera, the three pairs of legs are covered with scales. The membranes are covered with minute scales which have jagged ends or hairs and are attached by hooks. The wings are moved by the rapid muscular contraction and expansion of the thorax. In some Lepidoptera families such as the Psychidae and Lymantriidae, the wings are reduced or even absent (often in the female but not the male). File:Hemaris_diffinis_P1020035a.jpg|Hyaline patches on the wings of a hummingbird hawk-moth, the snowberry clearwing (Hemaris diffinis) File:Pachyerannis obliquaria1.jpg|Pachyerannis obliquaria, mating pair – winged male above, small wingless female below Venation . ''). Notice the bristle springing from the underside of the hindwing (frenulum) and running forward to be held in a small catch of the forewing, the function of which is to link the wings together. Tubular veins run through the two-layered membranous wing. Veins are connected to the haemocoel and in theory allow haemolymph to flow through them. In addition, a nerve and trachea may pass through the veins. In the basal Lepidoptera, the venation of the forewing is similar to that of the hindwing; a condition referred to as "homoneurous". The Micropterigidae (Zeugloptera) have venation that resembles the most primitive caddisflies (Trichoptera). All other Lepidoptera, the vast majority (around 98%), are "heteroneurous", the venation of the hindwing differing from that from the forewing and being sometimes reduced. Moths of the families Nepticulidae, Opostegidae, Gracillariidae, Tischeriidae, and Bucculatricidae, amongst others, often have greatly reduced venation in both wings. All but the most basal forms exhibit this wing coupling. There are three different types of mechanisms – jugal, frenulo–retinacular, and amplexiform. The more primitive groups have an enlarged lobe-like area near the basal posterior margin (i.e. at the base of the forewing) called a jugum, that folds under the hindwing during flight. == Scales ==

The wings of Lepidoptera are minutely scaled, which gives the name to this order; the name Lepidoptera was coined in 1735 by Carl Linnaeus for the group of "insects with four scaly wings". It is derived from Ancient Greek lepis (λεπίς) meaning "(fish) scale" (and related to lepein "to peel") and pteron (πτερόν) meaning "wing". Scales also cover the head, parts of the thorax and abdomen as well as parts of the genitalia. The morphology of scales has been studied by J. C. Downey and A. C. Allyn (1975) and scales have been classified into three groups, namely hair-like, or piliform, blade-like, or lamellar and other variable forms. this arrangement provides a stalk or pedicel by which scales are attached to the substrate. Scales may be piliform (hairlike) or flattened. The body or "blade" of a typical flattened scale consists of an upper and lower lamella with an air space in between. The surface towards the body is smooth and known as the inferior lamella. The upper surface, or superior lamella, has transverse and longitudinal ridges and ribs. The lamellae are held apart by struts called trabaculae and contain pigments which give colour. The scales cling somewhat loosely to the wing and come off easily without harming the butterfly. Colour The scales on butterfly wings are pigmented with melanins that can produce the colours black and brown. The white colour in the butterfly family Pieridae is a derivative of uric acid, an excretory product. Bright blues, greens, reds, and iridescence are usually created not by pigments but through the microstructure of the scales. This structural coloration is the result of coherent scattering of light by the photonic crystal nature of the scales. The specialised scales that provide structural colours to reflected light mostly produce ultraviolet patterns which are discernible in that part of the ultraviolet spectrum that lepidopteran eyes can see. The iridescent structural coloration on the wings of many lycaenid and papilionid species, such as Parides sesostris and Teinopalpus imperialis, and lycaenids such as Callophrys rubi, Cyanophrys remus, and Mitoura gryneus, has been studied. They manifest the most complex photonic scale architectures known – regular three-dimensional periodic lattices, that occur within the lumen of some scales. In the case of the Kaiser-i-Hind (Teinopalpus imperialis), the three-dimensional photonic structure has been examined by transmission electron tomography and computer modelling to reveal naturally occurring "chiral tetrahedral repeating units packed in a triclinic lattice", the cause of the iridescence. File:Morphocypris2.JPG|Structural blue colour in morpho cypris, a nymphalid File:Morphocyprislateral.JPG|When the same Morpho cypris specimen is seen end on, the blue colour turns black. File:Common_Jezebel_Delias_eucharis_edit_by_kadavoor.jpg|The white colour in pierids, such as Delias eucharis is a derivative of uric acid, an excretory product. File:Teinopalpus imperialis Male.jpg|The green iridescence of the swallowtail Kaiser-i-Hind (Teinopalpus imperialis) led to the discovery of three-dimensional photonic crystal structure. File:Colostygia_aqueata_Buchstein01.jpg|Wing coloration in certain Lepidoptera permits camouflage as can be seen in the case of the geometrid moth Colostygia aqueata. Function eyespot '', a nymphalid Scales play an important part in the natural history of Lepidoptera. Scales enable the development of vivid or indistinct patterns which help the organism protect itself by camouflage, mimicry, and warning. Besides providing insulation, dark patterns on wings allow sunlight to be absorbed and are probably involved in thermoregulation. Bright and distinctive colour patterns in butterflies which are distasteful to predators help communicate their toxicity or inedibility, thus preventing predation. In Batesian mimicry, wing colour patterns help edible lepidopterans mimic inedible models, while in Müllerian mimicry, inedible butterflies resemble each other to reduce the numbers of individuals sampled by inexperienced predators. Androconia Male Lepidoptera possess special scales, called androconia (singular – androconium), which have evolved as a result of sexual selection for the purposes of disseminating pheromones for attracting suitable mates. Androconia may be dispersed on the wings, body, or legs or occur in patches, referred to as "brands", "sex brands" or "stigmata" on the wings, usually in invaginations of the upper surface of the forewings, sometimes concealed by other scales. Androconia are also known to occur in the folds of wings. These brands sometimes consist of hairlike tufts which facilitate the diffusion of the pheromone. The role of androconia in the courtship of pierid and nymphalid butterflies, such as Pyronia tithonus and Dryas iulia, has been proven experimentally. Successive close-ups of the scales of a peacock wing == Abdomen ==

The abdomen or body is composed of nine segments. In the larva it ranges from segments 5 to 13. The eleventh segment of the larva holds a pair of anal claspers, which protrude in some taxa and represent the genitalia. The females of some moths have a scent-emitting organ located at the tip of the abdomen. The arrangement of genitalia is important in courtship and mating as they prevent cross-specific mating and hybridisation. The uniqueness of a species' genitalia led to the use of the morphological study of genitalia as one of the most important keys in taxonomic identification of taxa below family level. With the advent of DNA analysis, the study of genitalia has now become just one of the techniques used in taxonomy. File:Citheronia regalis closed claspers, MM.jpg|Citheronia regalis with claspers closed File:Citheronia regalis open claspers, MM.jpg|Citheronia regalis with claspers open File:Parnassius apollo - 01 (HS).jpg|Female Apollo with sphragis or mating plug File:Parnassius apollo - sphragis 02 (HS).jpg|Close up of the hardened sphragis extruding 2 to 3 mm behind the abdomen of Parnassius Cloaca Lepidopteran insects feature a cloaca at the end of the abdomen. This may be complete, incorporating the anus, the ovipore and the copulatory pore, as in the case of the Dacnonypha, Zeugloptera and the majority of the Monotrysia; or incomplete, incorporating the anus and ovipore only, as found in some of the Monotrysia, the Psychidae, and in some Choreutidae and Cossidae. == Development ==

The fertilised egg matures and hatches to give a caterpillar. The caterpillar is the feeding stage of the lepidopteran life cycle. The caterpillar needs to be able to feed and to avoid being eaten and much of its morphology has evolved to facilitate these two functions. After growth and ecdysis, the caterpillar enters into a sessile developmental stage called a pupa (or chrysalis) around which it may form a casing. The insect develops into the adult in the pupa stage; when ready the pupa hatches and the adult stage or imago of a butterfly or moth arises. Egg Like most insects, the Lepidoptera are oviparous or "egg layers". The cytoplasm is enclosed by the vitteline envelope and a proteinaceous membrane called the chorion protects the egg externally. The zygote nucleus is located posteriorly. The eggs of Lepidoptera are usually rounded and small (1 mm) though they may be as large as 4 mm in the case of Sphingidae and Saturniidae. They have a toughened (sclerotised) head capsule, mandibles (mouthparts) for chewing, and a soft tubular, segmented body, that may have hair-like or other projections, three pairs of true legs, and additional prolegs (up to five pairs). The larvae have silk glands which are located on the labium. These glands are modified salivary glands. They use these silk glands to make silk for cocoons and shelters. The abdominal spiracles are located on each side of the body on the first eight abdominal segments. Caterpillars undergo ecdysis and have a number of larval instars, usually five but varying between species. The new cuticle is soft and allows the increase in size and development of the caterpillar before becoming hard and inelastic. In the last ecdysis, the old cuticle splits and curls up into a small ball at the posterior end of the pupa and is known as the larval exuvia. File:Common mormon (Papilio Polyetes) catapillars.jpg|Two instars of the papilionid common Mormon with different camouflage schemes – resembling bird droppings and vegetation File:Stauropus fagi3.jpg|The larvae of notodontid moths, such as that of Stauropus fagi, have elongated thoracic legs. File:Taturana.JPG|The larva of Lonomia obliqua, a saturniid moth from Brazil, has urticating hairs with a lethal anticoagulant poison. File:Saddleback moth caterpillar.jpg|Saddleback moth (Acharia stimulea) larvae display aposematic colouring in the shape of a saddle. File:PhobUnderside.JPG|Underside of slug caterpillars of Phobetron pithecium (family Limacododiae) showing the absence of prolegs File:Phyllocnistis populiella damage2.jpg|Caterpillar of common aspen leafminer (Phyllocnistis populiella) File:Hypsipyla.jpg|The mahogany shoot-borer (Hypsipyla grandella) damages mahogany in Brazil. File:Family Psychidae444.jpg|Bagworm caterpillar (possibly Hyalarcta huebneri family Psychidae) emerging from its case File:Blue Mormon Larva.jpg|Last instar of blue Mormon larva-resembling vegetation Chrysalis or pupa showing parts '' A cocoon is a casing spun of silk by many moth caterpillars, and numerous other holometabolous insect larvae as a protective covering for the pupa. Most Lepidoptera larvae will either make a cocoon and pupate inside them or will pupate in a cell under the ground, The caterpillars of many butterflies attach themselves by a button of silk to the underside of a branch, stone, or other projecting surface. They remain attached to the silk pad by a hook-like process called a cremaster. Most chrysalids hang head downward, but in the families Papilionidae, Pieridae, and Lycaenidae, the chrysalis is held in a more upright position by a silk girdle around the middle of the chrysalis. During the pupal stage, the morphology of the adult is developed through elaboration from larval structures. Among the features discernible in the head region of a pupa are sclerites, sutures, pilifers, mandibles, eye-pieces, antennae, palpi, and the maxillae. The pupal thorax displays the three thoracic segments, legs, wings, tegulae, alar furrows, and axillary tubercles. The pupal abdomen exhibits the ten segments, spines, setae, scars of larval prolegs and tubercles, anal, and genital openings, as well as spiracles. The pupa of borers display the flange-plates while those of specialised Lepidoptera exhibit the cremaster. Besides this, all appendages and the body are separate from the pupal skin and enjoy a degree of independent motion. All other superfamilies of the Lepidoptera are more specialised, have non-functional mandibles, appendages and body attached to the pupal skin, and lose a degree of independent movement. File:Black_Swallowtail_Chrysalis_Megan_McCarty33.jpg|Papilionid chrysalids are typically attached to a substrate by the cremaster and with the head up held by a silk girdle. File:Common_crow_pupa.jpg|Suspended golden-coloured nymphalid chrysalis of Euploea core File:Actias luna emergence sjh stabilised.gif|Actias luna (family Saturniidae) emerging from cocoon File:Agrius convoluli (pupa).jpg|The specialised pupa of a sphingid moth, Agrius convolvuli, can wriggle its abdomen making a clicking sound, which can have a startle effect. == Defense and predation ==

'') resembles a dried leaf perfectly. butterfly, the common cerulean (Jamides celeno). These tails are thought to confuse a predator as to the location of the head thereby increasing the butterfly's chances of survival. '' family Papilionidae), the largest butterfly in the world, has bright colours and distinctive markings which advertise its inedibility. Lepidopterans are soft bodied, fragile, and almost defenseless while the immature stages move slowly or are immobile, hence all stages are exposed to predation by birds, small mammals, lizards, amphibians, invertebrate predators (notably parasitoid and parasitic wasps and flies) as well as fungi and bacteria. To combat this, Lepidoptera have developed a number of strategies for defense and protection which include camouflage, aposematism, mimicry, and the development of threat patterns and displays. Camouflage is an important defense strategy enabled by changes in body shape, colour, and markings. Some lepidopterans blend with the surroundings, making them difficult to be seen by predators. Caterpillars can be shades of green that match their host plant. Others resemble inedible objects, such as twigs or leaves. The larvae of some species, such as the common Mormon and the western tiger swallowtail look like bird droppings. Some species of Lepidoptera sequester or manufacture toxins which are stored in their body tissue, rendering them poisonous to predators; examples include the monarch butterfly in the Americas and Atrophaneura species in Asia. Predators that eat poisonous lepidopterans may become sick and vomit violently, and so learn to avoid those species. A predator who has previously eaten a poisonous lepidopteran may avoid other species with similar markings in the future, thus saving many other species as well. Toxic butterflies and larvae tend to develop bright colours and striking patterns as an indicator to predators about their toxicity. This phenomenon is known as aposematism. Aposematism has also led to the development of mimicry complexes of Batesian mimicry, where edible species mimic aposematic taxa, and Müllerian mimicry, where inedible species, often of related taxa, have evolved to resemble each other, so as to benefit from reduced sampling rates by predators during learning. Similarly, adult Sesiidae species (also known as clearwing moths) have a general appearance that is sufficiently similar to a wasp or hornet to make it likely that the moths gain a reduction in predation by Batesian mimicry. Eyespots are a type of automimicry used by some lepidopterans. In butterflies, the spots are composed of concentric rings of scales of different colours. The proposed role of the eyespots is to deflect predators' attention. Their resemblance to eyes provokes the predator's instinct to attack these wing patterns. The role of filamentous tails in Lycaenidae has been suggested as confusing predators as to the real location of the head, giving them a better chance of escaping alive and relatively unscathed. Some caterpillars, especially members of Papilionidae, contain an osmeterium, a Y-shaped protrusible gland found in the prothoracic segment of the larvae. When threatened, the caterpillar emits unpleasant smells from the organ to ward off the predators. == See also ==