Squirrels are non-aggressive however; they are capable of causing destruction. They dig up nuts and other items from the ground and they can leave huge holes in your yard. They can disrupt flowers and other vegetation and they can trample and eat out of your garden. If you have bird feeders, they may try to climb them and eat the birdseed or worse, lie in wait for an unsuspecting bird. They also like to chew on things including birdhouses.
Squirrels that get into homes will nest in the attic and they may gnaw and chew on wooden beams that support the ceiling and walls. They are dangerous to both themselves and to humans if they chew on electrical cords or wires. They frequently traverse power lines and this can lead to an electrical short if they cause damage to the wires.