While Squirrels have traditionally built their nests in the forks and cavities of trees, they now often make their homes inside attics. They are incredibly smart animals and have adapted well to urban environments.
Attics and soffit areas make ideal nesting locations for squirrels. They provide protection from predators and humans and allow the squirrels to stay warm and dry during inclement cold weather. Since squirrels can make their way into an attic through any hole no larger than 2 inches they often become uninvited guests in people's attics.
Using their powerful teeth, squirrels are easily capable of chewing through wood to create holes that allow not only themselves, but also rain to enter your home. Once inside, their nesting habits and fondness for gnawing down their incisors can cause thousands of dollars in building damage.
Like most animals, the usual reason a squirrel will invade an attic is because it is a female looking for a safe place to have and raise her offspring. Squirrels breed twice per year. In general, the first litter are born between March and May with the second litter born between July and August. The average litter contains between two and six babies.
Baby squirrels are born hairless and blind. They are immobile for the first six weeks of their lives and will not venture outside the den site for at least eight weeks. In that time, they are capable of creating quite the mess inside your attic.