"polyphemus geometrid" is a strange phrase, almost an oxymoron like "lead balloon".

Your moth cocoon is probably a polyphemus saturniid. Geometrids are typically smallish, dainty moths.

You should probably leave the cocoon alone. I think the pupa emits some liquid to help escape the cocoon when the time comes. The storage temperature will determine when the moth will emerge. The most important thing is to put the cocoon in a very large container, a cubic foot is not too large, and put in sticks or objects the moth can mount to open and dry its wings. Otherwise the wings will remain a crumpled mess and the moth cannot fly.

I had one in the garage in a box with some sticks and a screen over the top some years ago and it emerged just fine.

Polys are active while they are in their cocoons, especially if you bother them.

You did not say where you are at. If you are where it gets cold during the winter, I suggest you keep the cocoon in an unheated place until next April. Otherwise, there is a decent chance you will have a moth in the middle of the winter.

If you have it in a jar, make sure it has something it can climb on because the moth cannot crawl up smooth glass.

KC

Okay, thanks. I wasn't aware they could wiggle around so much while in the cocoon. I'll see if I can't keep him safe until next spring. =]

I appreciate the promptness in the replies. I've only recently got into collecting bugs and the like. Do you know of any good websites or other resources for bug metamorphosis? I can find only limited information; most of the sights I find don't go in-depth when it comes to breeding, transformation, and the fact that a caterpillar pretty much dissolves and is reconstructed from imaginal cells.

Thanks again! =D

http://www.cals.ncsu.edu/course/ent591k/trans.html is a start; highly technical scientific info on the web is usually presented as abstracts that require a fee to get the whole document.