While inspecting an attic for mice in North Stonington CT. today I noticed this.Carpenter ants will often end up inside a home when they already have a nest nearby outside. The foraging ants may start a satellite nest inside the home. Moisture in the home from clogged gutters, leaking plumbing and more can also be an attraction to the ants.
In this case, when I asked the homeowner if they had carpenter ants before, they replied that recently a contractor was taking off trim and siding above a large window where the wood was rotting with moisture. As he did a large ant nest was found to be behind the siding and around and in the window framing. A company came out to treat that spot for the ants the contractor had seen when he opened up the area around the window. When I looked at the board in the attic with the ant damage, it seemed like it was the only one, the other wood joists and rafters appeared to be sound. Then I realized how the damaged board inside was just on the other side of the exterior wall from that infested window area, outside. When disturbed, some of the ants likely quickly moved inside.
With spring comes ants. Call us if you see them in your home. We can inspect and treat the problem for you.