I found a big black fly in my enclosed bubbler

i wake up this morning to check up on my babies, lift the dome on the cloner and what do i see? a full grown (house?) fly nestling comfortably on one of the clones. how in the heck did it get there? was it born there? did it somehow sneak past my radar the night before? subzero temps outside, all the flies are dead? i haven't seen a fly in months. the thing didn't want to get off either, i had to push the thing before it flew onto another plant. is this common and am i in for an infestation?

p.s. my set up is inside my bedroom inside my closet.

I wouldn't worry about it. If I remember correctly, there are actually spores that are released during late fall that kill off flies. So even the ones that don't die from the cold, die from the spores. There are some flies that survive though, but they wont be able to create any sort of infestation that you would need to worry about.

I actually think the Government had something to do with it.

P.S. Don't look under your bed!!!!