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Although not a classification of insect by itself, the catepillar is a stage in the life form of many other insects -- from moths, to butterflies, to wasps. Despite the variety of insects that unique caterpillars may develop into, they still share a number of common traits.


 


Caterpillars have long segmented bodies with legs. They do not breathe through their mouths, but 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. Although they have poor eyesight and hearing, they do have a series of six tiny eyelets or 'stemmata' on the lower portion of their head, and rely on their antennae to help them locate food.


Camoupillars: 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.

Fighters: More aggressive self-defense 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.

Poisonpillars: 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.

Friendly communication: 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.

Big eaters: 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.

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