First thing you do is find the hole where it is getting in. Then, depending on what kind of rodent it is, you take different steps. If it’s a squirrel, you wait until it leaves the house in the morning to go to work and then you patch the hole so it can’t get back in. You do not want to do this if it has babies inside, but this is not the right time of the year for babies.
If it is a rat, you can patch the hole, but you don’t know if it lives in the house, or not, and you really don’t want to trap it inside. You do need to get rid of it, because it will lead more rats into the house or worse, have babies. You can set rat traps, but you have to get the rat the first time. If the trap goes off without catching the rat, then throw out the trap, because the rats are smart.
We just had a rat problem. We tried three different kinds of traps and it stayed away from all of them. Finally we called the pest lady. She told us we had to patch the wall where the rat was coming in (along the sewer line). That cost us $2500 because we also had to reparge the wall at the same time. It was only an eighth of the basement, at that.
The rat was still with us, so she said we had to lay out “bait.” Poison. We had not wanted to do that because we didn’t want the rat caught in a wall and smelling up everything while it decomposed. But we did what the pest lady said, and she laid out bait and the bait was eaten. We never saw the rat, nor smelled it, but it seems to be gone.
You could go to the poison right away, I guess. It would probably get whatever is up there.