This is a mouse highway into your house.
What is? A door? Trees overhanging the house and a roof vent? A hole beside a window?
It's where the AC lines attach to the house!
Typically these lines are near to the ground, or easily accessed by climbing mice from the unit.
They merely follow the trail into the house.
If they are allowed, that is!
How are they allowed?
When the putty, or whatever sealer, dries up and falls away. Look at the size of that opening! It is a magical, always-open door! They can come and go at will.
A mouse needs only a 1/4" gap or hole to get into a house! That is not much space! Once a group of mice find such an opening in a house they move in.
And once inside they will create bedrooms, find sources of food and water, and grow in numbers.
AND THEY WILL GROW IN NUMBERS!
My recommendation: look around the house for any sources that will allow critters to get in. This is basic home maintenance. Even the smallest holes should not be overlooked. A mouse might find a small hole and work to enlarge it. And again, once inside, they will move in the entire extended family, and create more.
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560