A moderate amount of weevils in feed not otherwise damp or moldy won't hurt them. A lot of weevils especially if the feed seems to be moldy or otherwise breaking down would be bad. When I have feed like that I use it for fertilizer where the birds can't get into it.
Insects that infest and eat the chicken feed. Can be one of a number of species of small beetles, moths, and likely other insect types that I haven't encountered.
my extra chicken feed is currently in the freezer. I faced a few nasty issues with parrot food a while back (moths, weevils, you name it it was in there) now I freeze everything. 24 hours for anything under 5lbs, 7 days for anything over 5lbs. Additionally having a small flock I freeze to extend shelf life- works with the parrot food, why not with the chickens?