Damage to Structures
Squirrels, being rodents, are known for their gnawing. The size of holes made by squirrels can be generalized. Fox and gray squirrels use holes the size of a baseball (Figure 5a). Red squirrels use holes the size of a golf ball. Flying squirrels use holes the size of a quarter. Squirrels often travel power lines and short out transformers. They gnaw on wires, enter buildings, and build nests in attics. They may chew holes through tubing used in maple syrup production. Feces of flying squirrels mixed with urine can cause stains (Figure 5b).
Damage to Livestock and Pets
Squirrels do not pose a threat to pets, but will consume eggs and nestlings. Flying squirrels are small enough to enter most bird houses and are likely to eat nestling birds.
Damage to Landscapes
Squirrels occasionally damage trees by chewing and stripping bark from branches and trunks. Pine squirrels damage Ponderosa pine, jack pine, and paper birch. In the Southeast, fox squirrels damage loblolly and other pines.
Tree squirrels may eat pine cones and nip twigs to the extent that they interfere with natural reseeding of important forest trees. This can be a problem in Ponderosa pine forests where pine squirrels may remove 60% to 80% of the cones in poor to fair seed years. In forest seed orchards, squirrel damage interferes with commercial seed production.
In nut orchards, squirrels can severely curtail production by eating nuts prematurely and by carrying off mature nuts. In fruit orchards, squirrels may eat cherry blossoms and destroy ripe pears. Pine, gray, and fox squirrels may chew the bark of various orchard trees.
Squirrels may damage lawns by burying or digging up nuts. They chew bark and clip twigs on ornamental trees or shrubbery planted in yards. Squirrels often take food at feeders intended for birds. Sometimes they chew to enlarge openings of bird houses and then enter to eat nestling songbirds. Squirrels may eat planted seeds, mature fruits, corn, and grains.
Health and Safety Concerns
Squirrels chew on electrical lines, leading to fires. If left long enough, their gnawing can weaken rafters.
Fox and gray squirrels are vulnerable to several parasites and diseases. Ticks, mange, fleas, and internal parasites are common. Squirrel hunters often notice bot fly larvae, called “wolves” or “warbles,” protruding from the skin, especially before frosts. The larvae do not impair the quality of the meat for eating and they are not known for harboring diseases dangerous to humans. The droppings of flying squirrels have been associated with murine typhus.