Critters of all kinds can cause problems: squirrels chewing through wiring and causing fires; squirrels chewing through auto wiring as parents had this happen twice to a neighbor in FL which required all wiring to be replaced. Mice can get into any area as long as they can get their head through as the body will compact. BTW, a local power company suggested putting a lock on the main breaker or fuse box which was outside for some reason. Kids would pull the breaker or fuse block, turning off power. What was even worse, they would toss the block in the trash somewhere. No poser until it was replaced.
Trivia: We hear of something having a bug in it. Well, in the early days, computers used contact switches. A mishap showed a bug had gotten between the contacts, rendering the computer useless. Since then, any problem is referred to as a bug in the system.