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Moth Cocoons

Moths of Pennsylvania

Moth Cocoons
 
During this winter, you may have had the relatively uncommon pleasure of finding a cocoon of a metamorphosizing moth. If you did, you should consider yourself lucky, because moth cocoons are fairly hard to find. Many make their cocoons underground, including Noctuid (Owlet) moths, as well as Sphinx (Hawk) moths. Others make theirs in the leaves on the ground surrounding the bases of trees, including some silk moths and various others. Still other make theirs hanging from trees, mainly silk moths. The ones hanging from trees can be somewhat conspicuous, although they are easily mistaken for dead leaves. Still, these are your best bets at locating a cocoon. If you haven't tried yet and wish to, now is the time since the leaves will soon be returning and making it very difficult to see the cocoons that hang from tree branches among the leaves. One of the easiest cocoons to find is the Promethea moth's cocoon, which is the Moth of the Week for 4-3-06.
Perhaps you have found a cocoon and have thought, how can such a small object house such a comparitively large insect? Well, if you have, you're not alone. I also thought that and therefore didn't expect the first Promethea cocoon I found to be a Promethea, based on the fact that a Promethea cocoon is approximately the size of your index finger in length and width, and the moth is 7.5 to 9.5 centimeters in wingspan! But, it fits all right.
It all works like this: the caterpillar goes into its last stage of molting, known as pupation, and raps itself in a dead leaf or silk it spins. It then turns to a liquid, completely "melting down." It then reforms into the shape of the moth it will become, but very constricted within the confines of its cocoon. While it is in there, its body is full of the fluid that will pump into its wings to keep them rigid once it emerges, and the body is thus very swelled. The wings are crumpled and bent around the body, which is how it fits inside the cocoon.
Written by Adam