Gray squirrels are primarily diurnal (active during the day). They generally mate in the fall and spring and have litters ranging from 2-6 with a gestation period of 1-2 months. They can have 2 litters a year. They have a very strong homing instinct and pass their nesting sites down from generation to generation. So the offspring will return to their birthplace to breed over and over again. Parenting is up to the adult females. Males do not take part in raising the young. Adult female gray squirrels are very territorial and do not allow any other male or female adult squirrels in their nesting area. Squirrels feed primarily on fruits, nuts, and seeds, but will eat insects, eggs, and other kinds of meat. Squirrels have adapted to living with humans and love to live in attics. They also love to chew, and will chew on houses, wires, ducts, and pipes. People don't like the noises of squirrels running about above the ceiling or in the eaves, but it's really the chewing that's a problem. If squirrels chew on electrical wires or water lines in an attic, it can create a real potential fire or flooding problem. Squirrels also bring in nesting material and leave urine and droppings in an attic. There are no real important diseases associated with squirrels, however, they do carry parasites, and thus are vectors for the diseases that fleas, ticks, and other insects can transmit. Their droppings pose the usual excrement health risks, such as leptospirosis or salmonella.
Flying squirrels are primarily nocturnal (active at night). They are the smallest of the tree squirrels. They usually breed in the fall and have a litter ranging from 2-6. They behave similar to Gray squirrels in feeding, but do have some differences in breeding. Parenting is a shared responsibility. Both the male and female squirrels take part in raising their young and it is common to have multiple flying squirrel families den together in the winter months. They cause the same problems Gray squirrels do other than being active at night.