Jenn............
If you go to an old neighborhood hardware store, look for a spray that contains chloropyrofos. It used to be sold under the trade name of "Dursban." You can spray it around the outside of your home (window frames, doors, etc.) and it will kill the critters that try to invade your home. It has a little odor, but I've even used it inside the home around the base boards, behind the fridge and stove, etc. If you have cats or dogs in the house, you should take them outside before treating and keep them out until the spray is dry. If you have fish tanks, turn off the filters and air pumps, cover the entire unit with a drop cloth. BIRDS MUST BE TAKEN OUT AND KEPT OUT UNTIL ALL SPRAY IS DRY AND THE ODOR HAS GONE! Avian lungs (parrots, etc.) are too delicate for even the odor!
Once the spray is dry, inside or out, it cannot be reactivated to harm your pets.
You more than likely brought that solitary critter into your home in something, but this spray will last for about 60 days without retreat so that if you happen to have others, they will be killed off as well.
Hope that this information helps you.