According to the FDA there can be insects or at least insect fragments in peanut butter.
I'm not sure how they get in there unless the insects are in the peanuts already and then when those peanuts get made into peanut butter the peanut butter then gets insects or at least insect fragments.
I've never found any insects in my peanut butter though but I guess they could be there but just hard to see them.
Even if your peanut butter contains or contained insects the insects are not harmful to your health.
Actually a lot of insects are nutritious for humans to consume and so you would actually be improving your health as most insects including ants are a good source of protein.