Brian Clink has the same question as i do. we found a mouse yesterday, it seem ok but my husband did notice something wrong with it's behind. and today it just laid in the box we had it in and you could see it's behind there was something coming out. not from it's butt it was more on it's under body. two spots (holes) on each side. it later died and we examined it more and my husband kind of pulled one out and it's some kind of bug. it was still moving and crawled around. we where thinking it ate this bug and the bug grew and started to eat the mouse from the inside out. it is football shaped, dark brown, looks like it has lot of leg ( i guess like a caterpiler but legs are shorter) just like Brian Clink discribed in his post.
Any idea what happened to this mouse?


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Nice find!  These are fly larvae, probably of the family Sarcophagidae - the flesh-flies.  Adults lay their eggs on mammals, usually in existing wounds but sometimes in skin folds or where fur is matted with dung, and the larvae hatch and burrow into the subcutaneous fat, eating their way through the tissues until fully grown, at which point they tunnel out, as you saw, and pupate in the soil.

Assuming you're in the UK, there's a recording scheme for the flesh-flies - details can be found at … ice=94 and the scheme organiser will be able to tell you more, particularly if you send him the specimens