OPEE was in the side wall of my basement for sometime before I found out. You guessed it...a possum. I kept hearing a pop sound along that outside wall. Couldn't find any sign of a critter of any kind. coming home from my quilt guild at 10:00pm i saw something run across the lawn and disappear. He went under my front steps. Called the enviornmental guy and 2 months and about $2000 and we THINK he is gone. If there was a 'HE' you know there would be a 'She' soon and they have babies in the spring. Long story short; it is the only marsupial in North America and my homeowners will cover the damage. They will not pay for removal but will cover the damage. He/she/it was running along the outside wall at the top of thr basement behind the insulation. This was all just in the last 3 months. I HOPE WE SOLVED THE PROBLEM and don't have anymore critters. The guy sealed the edge of the front steps with that expanding insulation stuff.
At first I was afraid but he/she/it never came into any other part of the house.