Insect and Spider Identification: CLOSED: Can you tell me what came out of this cocoon?, 1 by onalee

onalee wrote:
I found several of these empty cocoons in a small oak tree in my yard. At first, I thought they were bird nests of some kind, but with about 7 in one tree, I don't think so. I opened one up (had to use scissors, you can't tear them!) and found stuff in them like a bug of some kind had hatched (that kind of brown, thin, shell-like stuff).

The cocoons are hanging on small branches in the tree, there is a hole in the top of it where whatever was in it exited. They are smooth like brown paper sacks inside and out and between the 'paper' is a really tough web like material.

Can anyone tell me WHAT might have hatched - not sure whether to spray the tree or leave it alone (good bugs or bad bugs?)

Thanks for any direction you can give!

Onalee