D.L.
We had that happen in the house we rented several years back. It was an older home. Only 3 snakes got in that we knew of and they were garden snakes, harmless and my daughter actually kept 2 of them as pets for a while and we let them go in the forest right before winter set in.
Don't know how they got in but since it was no big deal to us - we just let it go.
Good Luck!
D.
Northern Black Hills