Will they leave on their own?
The squirrels might eventually leave but not for months. Waiting for these critters to leave is subjecting the property to significant and expensive damage. Squirrels can rip apart electrical wiring, ruin drywall, destroy air conditioning duct work, and the most obvious: leave feces and urine everywhere. If you allow them to leave on their own, there is a very likely possibility that the openings used by the squirrels will be found by other wildlife, and the damages will continue.
A quick and general way to determine what is nesting in your home or building is sound. Squirrels are active during the day and early evening hours, and sleep at night. Rats and flying squirrels are nocturnal- their most active hours will be at night.
Squirrel nests are always messy, and loosely constructed of different materials such as twigs, leaves, moss, and shredded bits from homes. These nests are usually found in the soffit.
Squirrel in trap
What happens if a squirrel reproduces in my attic?
Squirrels have two litters per year. The first between February-April, and the second in August-September. The common litter is usually between 2-3 young, but can birth up to 9. The litter usually does not venture out of the nest for about 7-8 weeks.
Squirrels will destroy your air conditioning duct work, rip apart electrical wiring, gnaw on plumbing, and ruin the dry wall. They leave their feces and urine in and throughout the insulation and in bad infestations will produce a strong and sometimes unbearable smell. Squirrel removal is essential to prevent costly damage in an attic.