[6][7] Widely introduced to certain places around the world, the eastern gray squirrel in Europe, in particular, is regarded as an invasive species.

[8] This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union.

[9] Sciurus carolinensis is native to the eastern and midwestern United States, and to the southerly portions of the central provinces of Canada.

[3] Breeding eastern gray squirrels are found in Nova Scotia, but whether this population was introduced or came from natural range expansion is not known.

Melanistic squirrels appear to exhibit a higher cold tolerance than the common gray morph; when exposed to −10 °C, black squirrels showed an 18% reduction in heat loss, a 20% reduction in basal metabolic rate, and an 11% increase to non-shivering thermogenesis capacity when compared to the common gray morph.

Their skin may become rough, blotchy, and prone to hair loss due to the mite parasite during the chilly winter months.

[33] Like many members of the family Sciuridae, the eastern gray squirrel is a scatter-hoarder; it hoards food in numerous small caches for later recovery.

They do this by preparing the spot as usual, for instance, digging a hole or widening a crack, miming the placement of the food, while actually concealing it in their mouths, and then covering up the "cache" as if they had deposited the object.

[37][38] Eastern gray squirrels build a type of nest, known as a drey, in the forks of trees, consisting mainly of dry leaves and twigs.

The dreys are roughly spherical, about 30 to 60 cm in diameter and are usually insulated with moss, thistledown, dried grass, and feathers to reduce heat loss.

They may also nest in the attic or exterior walls of a house, where they may be regarded as pests, as well as fire hazards due to their habit of gnawing on electrical cables.

[24][40] The first litter is born in February or March, the second in June or July, though, again, bearing may be advanced or delayed by a few weeks depending on climate, temperature, and forage availability.

[18] If a female fails to conceive or loses her young to unusually cold weather or predation, she re-enters estrus and has a later litter.

[44] The use of vocal and visual communication has been shown to vary by location, based on elements such as noise pollution and the amount of open space.

However, in heavily wooded areas, vocal signals are used more often due to the relatively lower noise levels and a dense canopy restricting visual range.

[45] In the wild, eastern gray squirrels can be found inhabiting large areas of mature, dense woodland ecosystems, generally covering 100 acres (40 hectares) of land.

[40] These forests usually contain large mast-producing trees such as oaks and hickories, providing ample food sources.

[49] Eastern gray squirrels predators include hawks, weasels, raccoons, bobcats, foxes, domestic and feral cats, snakes, owls, and dogs.

[53] Eastern gray squirrels eat a range of foods, such as tree bark, tree buds, flowers,[54] berries, many types of seeds and acorns, walnuts, and other nuts, like hazelnuts (see picture) and some types of fungi found in the forests, including fly agaric mushrooms[55] and truffles.

[56] Mast-bearing gymnosperms such as cedar, hemlock, pine, and spruce are another food source,[54] as well as angiosperms such as hickory, oak, and walnut.

[58] Eastern gray squirrels have a high enough tolerance for humans to inhabit residential neighborhoods and raid bird feeders for millet, corn, and sunflower seeds.

[59] However, in the UK eastern gray squirrels can take a significant proportion of supplementary food from feeders, preventing access and reducing use by wild birds.

By the turn of the 20th century, breeding populations of the eastern gray squirrel had been introduced into South Africa, Ireland, Italy, Australia (extirpated by 1973), and the United Kingdom.

[62] In South Africa, though exotic, it is not usually considered an invasive species owing to its small range (only found in the extreme southwestern part of the Western Cape, going north as far as the small farming town of Franschhoek), as well because it inhabits urban areas and places greatly affected by humans, such as agricultural areas and exotic pine plantations.

[66] In 1921 it was reported in The Times that the Zoological Society of London had released eastern greys to breed at liberty in Regents Park: A dozen years ago the Zoological Society of London obtained a number from a private collection in Bedfordshire for the purpose of inducing them to breed at liberty in the Gardens in Regent's Park.

After two or three years in which they seemed to be disappearing, they suddenly became ubiquitous...The grey squirrels are plainly happy and plainly give happiness to Londoners...On the other hand, grey squirrels, whether by taking advantage of tubes and buses, or by deliberate human connivance, have spread from London and are invading the country over very wide areas.

Gray squirrels were eaten in earlier times by Native Americans and their meat is still popular with hunters across most of their range in North America.

[69] In Britain and Ireland, the eastern gray squirrel is not regulated by natural predators,[70] other than the European pine marten, which is generally absent from England and Wales.

[71] This has aided its rapid population growth and has led to the species being classed as a pest and it is now illegal to release captured eastern grey squirrels back into the wild in the UK.

Ironically, "fears" for the future of the eastern gray squirrel arose in 2008, as the melanistic form (black) began to spread through the southern British population.