Are they weevils? I think that’s what they’re called. Those come from hay. I’ve found one or two in some bags of Oxbow before.
Can you look around your rabbit’s tummy and backside and see if you find any bumps or holes which indicate bug burrowing? Any ill health behaviors?
Rabbits are very clean animals, so typically bugs come from the hay or are attracted by unclean environments like a litter box that’s gone too long without being cleaned or a portion of a hutch overlooked and has been accumulating gross dirt over time.
Rabbits really do not attract bugs like that, so the more additional information you can provide, the better! If you can find one and capture it, take a picture, and post it, maybe we can identify a specific source. I recommend looking through hay containers and vessels first.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.