Caterpillar
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Image:Caterpillar at 5th stage.jpg
- This article is about insect larva. For information about the construction equipment corporation, see Caterpillar Inc.
A caterpillar is the larva form of a lepidopteran (a member of the insect order comprising butterflies and moths).
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Anatomy
Caterpillars have long segmented bodies. They have six legs, up to four pairs of prolegs on the middle segments of the abdomen, and sometimes a single pair of prolegs on the last abdominal segment. The sawfly larva (Hymenoptera) superficially resembles a caterpillar, but can usually be distinguished because the caterpillar has a gap between true legs and prolegs, whereas the sawfly does not. Another difference is that lepidopteran caterpillars have crochets or hooks on the prolegs. The gap between the prolegs and the true legs can vary from a slight gap in some species to a large gap in families such as the geometridae. The geometrids, also known as inchworms or loopers, are so named because of the way they locomote, appearing to measure the earth (the word 'geometrid' means 'earth-measurer' in Greek).
Image:Monarchcatterpillarsm.jpg
Caterpillars do not breathe through their mouths. Air enters their bodies through a series of small tubules along the sides of their thorax and abdomen. These tubules are called 'spiracles', and inside the body they connect together into a network of airtubes.
Caterpillars do not have very good eyesight or senses. Rather than having fully-developed eyes they have a series of six tiny eyelets or 'stemmata' on the lower portion of their head. They rely on their antennae to help them locate food.
Defence
Many species of birds and animals consider caterpillars to be a tasty protein snack, so the caterpillars have evolved several methods of protecting and/or camouflaging themselves. These methods can be either passive, aggressive, or both. Some caterpillars have large 'false eyes' towards the rear of their abdomen. This is an attempt to convince predators that their back is actually their front, giving them an opportunity to escape to the 'rear' when attacked. Others have a body coloration that closely resembles their food plant.
More aggressive self-defence measures are taken by the spitfires and hairy caterpillars. These caterpillars have spiny bristles or long fine hairs that will irritate anything that brushes against them, or spit acidic digestive juices at potential enemies. However, some birds, like cuckoos, will swallow the hairiest of caterpillars.
Some caterpillars eat the leaves of plants that are toxic to other animals. They are unaffected by the poison themselves, but it builds up in their system, making them highly toxic to anything that eats one of them. These toxic species, such as the Cinnabar moth (Tyria jacobaeae) caterpillars, are brightly striped or coloured in red and yellow - the 'danger' colours.
The aim of all these aggressive defense measures is to assure that any predator that eats (or tries to eat) one of them will not be in a hurry to repeat the experience.
Some caterpillars obtain protection by associating themselves with ants. The Lycaenid butterflies are particularly well known. Recent findings have shown that they communicate with their ant protectors by means of vibrations as well as chemical means.
Behavior
Image:Snodgrass Schizura concinna.jpg Caterpillars have rightfully been called eating machines. They eat leaves voraciously, shed their skins generally four or five times, and eventually pupate into an adult form. Caterpillars have the fastest growth rate of any animal in the world. For instance, a tobacco hornworm will increase its own weight ten thousand times in less than twenty days. One of their adaptations that enables them to eat this much is a mechanism in a specialized midgut which transports ions at a very high rate to the lumen (midgut cavity), to keep the potassium level higher in the midgut cavity than in the blood. This mechanism is not found in any vertebrates.
"Tiny, snail-eating caterpillars found in Hawaiian rain forests tie up their prey with sticky silk and snack on them at leisure. [...] It is the first time that caterpillars that eat snails or any other mollusk have been found."
Other carnivorous species of caterpillars are also known, but still represent a tiny fraction of all known representatives of these insect larvae. Template:Clear
See also
Larva Locomotion: A Closer Look —- video clips show how monarch larvae walk. More video clips from nature
3D animation Papilio polyxenes larvae walking.
Photo gallery
 Cup Moth |
 Cup Moth on bicycle wheel |
 Caterpillar |
 Xylena exsoleta |
 Xylophanes tersa |
 Pale Tussock Moth Caterpillar |
 Caterpillar |
 A file of processional caterpillars |
 Woolly Bear |
 Polyphemus moth |