Squirrels are abundant in the wilds due to their natural predators being less abundant. Because of this population increase and a decreasing natural habitat due to construction, we are seeing them progressively more in our attics. They seek warm, safe shelter during the fall and winter months in particular. Squirrels tend to gnaw on wood and electrical wiring causing destruction and fires. It also is common for them to fall into vents and chimneys on the roof, or possibly find their way into wall voids, where they may die and cause odor and pest problems. They may enter through openings only 1.5 inches wide as juveniles.
Squirrels born in attics are known to return to have their babies as well.