A cocoon is a silk spun covering
that the caterpillar makes. It protects the moth from nature and also helps
retain moisture. There are many different colors and types of cocoons. Some
cocoons are spun directly to the tree branch. There are also the caterpillars
that spin their cocoon in the leaves. This type falls to the ground in the winter.
The last and probably most annoying cocoon type is the one spun inside the creases
of the sleeve or net. These can be a pain to get out and you must be careful
not to damage the pupa inside of the cocoon.
After spinning a cocoon, the caterpillar
will make a pre-pupa. A pre-pupa is the phase in which the caterpillar shrivels
up and can no longer eat or walk. About four days later the caterpillar forms
a pupa. The pupa is the place where the actual moth forms. It will crack out
of this case in the spring and then have the trying task of escaping the cocoon.
This process of hatching out of the pupa and the exiting the cocoon is called
eclosure.
I usually cut my cocoons open. By
doing this I make sure the moth will eclose properly and nothing will happen
to it when it is trying to exit the cocoon. It is also beneficial when taking
photos. I caution beginners not to try cutting the cocoon until they have seen
someone else do it or have been raising moths for a couple of years.
There are also cocoons that diapause,
or stay as a cocoon overwinter, and then those that hatch out in three or four
weeks. Usually, first brood luna and polyphemus will hatch in three to four
weeks. First brood are those that make there cocoon in early summer and then
hatch for a second brood or generation. Cynthia ricini are an exception to this
rule and will hatch whenever they feel ready no matter the cold or moisture
content. The other silkmoths native to the United States usually will stay dormant
as a cocoon until the following spring.
