Worms and Flowers

An Instar is Born

Posted in Bugs by Lzyjo on October 1, 2009

Caterpillars are remarkable little creatures. They are the competitive eaters of the insect world, each a connoisseur,  specializing in a limited group of favorite plants.

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Second Instar

They start as miniscule eggs and emerge as a tiny prickly-looking caterpillars less than .5 inch  (1.3 cm) long. Caterpillars are technically larvae, but caterpillar sounds much cuter doesn’t it? After all it comes from Ango-French and Middle English words meaning hairy cat!

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Third Instar

Caterpillars are incredibly hungry and fast growing. Undergoing five stages of growth called instars. They get as fat as possible then molt their exoskeleton four times until they are officially pupa. Instead of shedding their exoskeletons, the new layer is “digested” and reabsorbed, probably a move to save energy, since caterpillars only purpose is to eat as much as possibly, as quickly as possible.

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Fourth Instar

Caterpillars are peculiar. They are so tiny, yet they move with amazing intricacy. They are muscle bound eating machines. I know, they don’t look like muscle men, but they are. Each caterpillar has 4,000 muscles that allows its body in the strangest ways, like when they hang way out from a limb, searching and searching for something to grab on to. Caterpillars have more muscles on their head (248) than we have bones in your bodies.  (206)

For being such small creatures, caterpillars display a variety of defense mechanisms from the intriguing to deadly. A certain species of South American silk worm has barbed hairs, similar to the tarantulas, which contain a venomous anticoagulant powerful enough to cause death by uncontrolled bleeding in humans.

Aside from their camouflage appearances, they have an arsenal of tricks to ward of potential predators. The swallowtail caterpillar has a unique defense mechanism. When threatened the caterpillars emit a distinctly pungent pheromone from a pair brightly colored, orange or red glandular organs called the osmeterium, which resemble antennae and spring out of the head.

Can you see? This one is really chomping away! It is very close to being a pupa, one more molt and it will be a mature pupa, ready to find a safe place to make a chrysalis. Don’t they change remarkably, in such a short time?

Since I’m not an insectologist (oh, I just wanted to say that word!) check my sources:

Wikipedia Butterflies good overview

Butterfly School Metamorphosis great photos of every stage

Monarch Butterfly “What is an Instar?” explanation of molting

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