Problems Squirrels may cause:

Red squirrels often enter buildings and stored vehicles to build nests.  They may damaging the building or vehicle to gain entry. Once inside they gnaw on electrical wires, woodwork and insulation. The dry grass they bring in for nesting material and the exposed wires can often cause a fire hazard. 

They can also store flammable material in the engine compartment of vehicles and stored RVs.

Squirrels are known to carry numerous diseases and parasites such as fleas, ticks, and mites, though only a few are dangerous to humans. Some of the more common include tularemia, typhus, plague, and ringworm. Such diseases are transmitted through bites or other forms of direct contact with infected squirrels. Tularemia, typhus, and plague have symptoms that mimic the flu and can be deadly when left untreated.

Squirrels occasionally damage lawns by burying, searching for and digging up nuts. They will chew bark and clip twigs on ornamental trees or shrubbery planted in gardens. Often squirrels take food at feeders intended for birds. They chew to enlarge openings of bird houses, entering to eat nestling songbirds. In gardens, squirrels may eat planted seeds, mature fruits, or grains crops such as corn.

Squirrels live in drays constructed of grass and twigs high up in trees and breed March-May, August-September producing usually 2-5 young. The gestation period is 33-35 days and the young are independent by 7-8 weeks old. For 70 days the mother provides milk for her young, and then they are cast out of the dray to seek their own territory. They become reproductively mature at the age of 1 year but are still developing. They can live for 5 to 10 years in the wild and have a top speed of 22.5 KM/H.

In residential areas, squirrels sometimes travel powerlines, shorting out transformers.

Squirrels may occasionally damage forest trees by chewing bark from branches and trunks. Pine squirrels damage Ponderosa pine, jack pine, and paper birch. This is a particular problem in Ponderosa pine forests where pine squirrels may remove 60% to 80% of the cones in poor to fair seed years. In nut orchards, squirrels can severely curtail production by eating nuts prematurely and by carrying off mature nuts. In fruit orchards, pine squirrels may eat ovaries of cherry blossoms and destroy ripe pears.