Lepidoptera ( ) or lepidopterans are an order of winged insects which include butterflies and moths. About 180,000 species of the Lepidoptera have been described, representing 8.6% of the total described species of living organisms, making it the second largest insect order (behind Coleoptera) with 133 families and 43 superfamilies, and one of the most widespread and widely recognizable insect orders in the world.
Lepidopterans have several distinctive features, especially colored scales that cover their bodies, large triangular wings, and a proboscis for drinking nectar. Almost all species have membranous wings. Mating and egg-laying are normally near or on host plants for the larvae. Butterflies and moths undergo complete metamorphosis. The larva is called a caterpillar; it has a cylindrical body with a well-developed head, chewing mouthparts, three pairs of legs and up to five pairs of prolegs. As it grows, it changes in appearance, going through a series of stages called instars. Once mature, it develops into a pupa. A few butterflies and many moth species spin a silk casing or cocoon for protection prior to pupating, while others just go underground. A butterfly pupa, called a chrysalis, has a hard skin, usually with no cocoon. In the pupa, metamorphosis occurs, and a sexually mature adult emerges.
Lepidopterans first appeared in the fossil record at the Triassic-Jurassic boundary. They have coevolved with flowering plants since the angiosperm boom in the Cretaceous. They have evolved a wide range of wing patterns ranging from camouflaged moths to the vivid displays of butterflies. A person who studies this order is called a lepidopterist.
Butterflies and moths are mostly herbivorous as caterpillars and nectar-feeding as adults. They serve as economically useful pollinators; conversely, caterpillars are often pests in agriculture, as they can quickly consume large quantities of leaves. Females often produce up to 600 eggs.
Etymology
The term Lepidoptera was used in 1746 by Carl Linnaeus in his Fauna Svecica. The word is derived from Greek , gen. ("scale") and ("wing")., . The word "butterfly" is from Old English , possibly from the pale butter color of some species' wings. The word "moth" is from Old English from Common Germanic and German meaning "moth". The word "caterpillar" is from Middle English , , probably an alteration of Old North French (from Latin , "cat" + , "hairy").
Distribution and diversity
The Lepidoptera are among the most successful groups of insects. They are found on all continents, except Antarctica, and inhabit all terrestrial habitats ranging from desert to rainforest, from lowland grasslands to mountain plateaus, but almost always associated with higher plants, especially angiosperms (flowering plants). Among the most northern dwelling species of butterflies and moths is the Siberian Apollo (Parnassius arcticus), found in the Arctic Circle in northeastern Yakutia, at an altitude of above sea level. In the Himalayas, Apollo species such as Parnassius epaphus occur up to an altitude of .
Some species are commensal or parasitic, inhabiting the bodies of organisms rather than the environment. Coprophagous pyralid moths, called sloth moths, such as Bradipodicola hahneli and Cryptoses choloepi, are unusual in that they are exclusively found in the fur of sloths. Two species of Tinea moths feed and breed on the horns of cattle. The larva of Zenodochium coccivorella is an internal parasite of Kermes scale insects. Many species breed in materials such as owl pellets, bat caves, honeycombs or diseased fruit.
As of 2007, there were roughly 174,250 lepidopteran species described, with butterflies estimated to comprise around 17,950, and moths making up the rest. The vast majority live 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, while Australia has about 400 species of butterflies and 14,000 species of moths. The diversity 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:
+ Diversity of Lepidoptera in each faunal regionPalearcticNearcticNeotropicAfrotropicIndo-Australian(comprising Indomalayan, Australasian, and Oceanian realms)Estimated number of species22,46511,53244,79120,49147,287
External morphology
Lepidoptera are morphologically distinguished from other orders by the presence of scales on 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 greater than , such as Queen Alexandra's birdwing and Atlas moth.
Head
The head houses sensing organs and mouthparts. Like the adult, the larva has a toughened, or sclerotized head capsule.Scoble (1995). Section The Adult Head – Feeding and Sensation, (pp. 4–22). Here, two compound eyes, and chaetosema, clusters of sensory bristles unique to Lepidoptera, occur, though many taxa have lost one or both of these clusters. The antennae vary widely in form among species and between the sexes. The antennae of butterflies are usually club-shaped, those of the skippers are hooked, while those of moths have segments variously enlarged or branched.
The maxillary galeae are modified to form an elongated proboscis. It consists of one to five segments, kept coiled up under the head by small muscles when it is not being used to suck up nectar from flowers.
The larvae, called caterpillars, have a toughened head capsule. Caterpillars lack the proboscis and have separate chewing mouthparts. 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 a group of up to six simple eyes.
Thorax
The thorax is made of three fused segments, the prothorax, mesothorax, and metathorax, each with a pair of legs. In some males of the butterfly family Nymphalidae, the forelegs are greatly reduced and are not used for walking or perching. Lepidoptera have olfactory organs on their feet, which help them to "taste" or "smell" their food.
The two pairs of wings are on the middle and third segments, or mesothorax and metathorax, respectively. In the more recent genera, the wings of the second segment are much more pronounced, while 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 has more powerful muscles to propel the moth or butterfly through the air, with the wing of this segment (forewing) having a stronger vein structure. The largest superfamily, the Noctuoidea, has its wings modified as hearing organs.
The caterpillar has an elongated, soft body that may have hair-like scales, three pairs of true legs, with none to 11 pairs of abdominal prolegs (usually eight) with hook-like spines for gripping called crochets. The thorax usually has 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, which instead have a form of gills.
Abdomen
The abdomen, less sclerotized than the thorax, consists of 10 segments, the first sometimes reduced. The last two segments form the external genitalia. The genitalia are highly varied, and distinguish the species. The females of basal moths have only one sex organ, which is used for copulation and as an ovipositor, or egg-laying organ. About 98% of moth species have a separate organ for mating, and an external duct that carries the sperm from the male.
The abdomen of the caterpillar has four 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 completely absent in other groups more adapted to boring (e. g., Prodoxidae) or living in sand (e.g. Nepticulidae).
Scales
Much of the body is covered with minute scales. Most are lamellar, or blade-like, and attached with a pedicel.Scoble (1995). Section Scales, (pp. 63–66). The surface of the lamella has a complex structure. It gives color through structural coloration, and may also be pigmented. Scales function in insulation, thermoregulation, producing pheromones (in males only), and aiding gliding flight, but the most important is the large diversity of patterns they create, enabling camouflage, mimicry, signalling to rivals, and potential mates. Hair-like (filamentous) scales around the head and abdomen are common, especially in moths.
Internal morphology
Reproductive system
In the reproductive system of butterflies and moths, the male genitalia are complex. In females the three types of genitalia are named for the associated moth clades: 'monotrysian', 'exoporian', and 'ditrysian'. In the monotrysian type there is an opening on the fused segments of the sterna 9 and 10, which allows insemination and oviposition. In the exoporian type (in Hepialoidea and Mnesarchaeoidea) there are separate places for insemination and oviposition, both on the same sterna as the monotrysian type, i.e. 9 and 10. The ditrysian groups have an internal duct that carries sperm, with separate openings for copulation and egg-laying. In most species, the genitalia are flanked by two soft lobes, although they may be specialized and sclerotized in some species for ovipositing in areas such as crevices and inside plant tissue. The glands that produce hormones drive development as the insects go through their life cycles. The first insect hormone prothoracicotropic hormone (PTTH) operates the species life cycle and diapause. It is produced by corpora allata and corpora cardiaca, where it is stored.
Digestive system
In the digestive system, the front of the foregut is modified to form a pharyngeal sucking pump for feeding on liquids such as nectar. The esophagus leads to the posterior of the pharynx and in some species forms a form of crop. The midgut is short and straight, while the hindgut is longer and coiled. Ancestral lepidopterans, stemming from Hymenoptera, had midgut ceca, not present in current butterflies and moths. Instead, 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. The goblet cells excrete positive potassium ions, absorbed from leaves ingested by the larvae. Most lepidopterans display the usual digestive cycle, sometimes adapted for specialised diets. Some, like the luna moth, exhibit no digestive system whatsoever; they survive as adults from stored energy consumed as larvae and live for no longer than 7–10 days..
Circulatory system
The circulatory system uses hemolymph, insect blood, for thermoregulation, taking heat from the muscles and transferring it to the rest of the body. 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.
Respiratory system