page_title: External morphology of Lepidoptera
section_title: Caterpillar
hierarchical_section_title: External morphology of Lepidoptera / Development / Caterpillar
caption_attribution_description: Papilio machaon Français&#160;: Photothèque personnelle de Hamon JP, auteur de ce cliché réalisé en cage d'élevage en Basse-Normandie. Chenille de Papilio machaon inquiète faisant saillir son osmétérium (glande odorante) pour impressionner son agresseur éventuel. Chenille nourrie aux fanes de carottes de jardin.
context_page_description: The external morphology of Lepidoptera is the physiological structure of the bodies of insects belonging to the order Lepidoptera, also known as butterflies and moths. Lepidoptera are distinguished from other orders 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 millimetres long, to a wingspan of many inches such as the Atlas moth. Comprising over 160,000 described species, the Lepidoptera possess variations of the basic body structure which has evolved to gain advantages in adaptation and distribution.
  Lepidopterans undergo complete metamorphosis, going through a four-stage life cycle: egg, larva or caterpillar, pupa or chrysalis, and imago / adult. The larvae – caterpillars – have a toughened head capsule, chewing mouthparts, and a soft body, that may have hair-like or other projections, three pairs of true legs, and up to five pairs of prolegs. Most caterpillars are herbivores, but a few are carnivores or detritivores.
context_section_description: Caterpillars, are "characteristic polypod larvae with cylindrical bodies, short thoracic legs and abdominal prolegs (pseudopods)". 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 body consists of thirteen segments, of which three are thoracic (T1, T2, and T3) and ten are abdominal (A1 to A10).
  All true caterpillars have an upside-down Y-shaped line that runs from the top of the head downward. In between the Y-shaped line lies the frontal triangle or frons. The clypeus, located below the frons, lies between the two antennae. The labrum is found below the clypeus. There is a small notch in the centre of the labrum with which the leaf edge engages when the caterpillar eats.
  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. Located below the labrum are the mandibles. On each side of the head there are usually six stemmata just above the mandibles. These stemmata are arranged in a semicircle. Below the stemmata there is a small pair of antennae, one on each side.
  The thorax bears three pairs of legs, one pair on each segment. The prothorax (T1) has a functional spiracle which is actually derived from the mesothorax (T2) while the metathorax has a reduced spiracle which is not externally open and lies beneath the cuticle. The thoracic legs consist of coxa, trochanter, femur, tarsus, and claw and are constant in form throughout the order. However they are reduced in the case of certain leaf-miners and elongated in certain Notodontidae. In Micropterigidae, the legs are three-segmented, as the coxa, trochanter, and femur are fused.
  Abdominal segments three through six and ten may each bear a pair of legs that are more fleshy. The thoracic legs are known as true legs and the abdominal legs are called prolegs. The true legs vary little in the Lepidoptera except for reduction in certain leaf-miners and elongation in the family Notodontidae. The prolegs contain a number of small hooks on the tip, which are known as crochets. The families of Lepidoptera differ in the number and positioning of their prolegs. Some larvae such as inchworms (Geometridae) and loopers (Plusiinae) have five pairs of prolegs or less, while others like Lycaenidae and slug caterpillars (Limacodidae) lack prolegs altogether. In some leaf-mining caterpillars there are crochets present on the abdominal wall which are reduced prolegs, while other leaf-mining species lack the crochets entirely. The abdominal spiracles are located on each side of the body on the first eight abdominal segments.
  Caterpillars have different types of projections; setae (hairs), spines, warts, tubercles, and horns. The hairs come in an assortment of colours and may be long or short; single, in clusters, or in tufts; thinner at the point or clubbed at the end. A spine may either be a chalaza (having a single point) or a scolus (having multiple points). The warts may either be small bumps or short projections on the body. The tubercles are fleshy body projections that are either short and bump like or long and filament like. They usually occur in pairs or in a cluster on one or more segments. The horns are short, fleshy, and are drawn to a point. They are usually found on the eighth abdominal segment.
  A large number of species of families Saturniidae, Limacodidae, and Megalopygidae have stinging caterpillars which have poisonous setae, called urticating hairs, and in the case of Lonomia – a Brazilian saturniid genus – can kill a human due to its potent anticoagulant poison. Caterpillars of many taxa that have sequestered toxic chemicals from host plants or have sharp urticating hair or spines, display aposematic colouration and markings.
  Caterpillars undergo ecdysis and have a number of larval instars, usually five but varying between species. The new cuticle is soft and allows the i
caption: Old World swallowtail caterpillar everting its osmeterium in defence
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