Gray squirrels are native to the eastern half of North America, where they’ve lived in hardwood forests for millions of years. Their scientific name, Sciurus carolinensis, reflects those southeastern U.S. roots. But the reason you might be asking this question is probably because gray squirrels now live in places they clearly don’t belong: the UK, Italy, South Africa, and beyond. Every one of those populations traces back to deliberate human introductions, mostly during the late 1800s and early 1900s.
Native Range in North America
Gray squirrels evolved in the broadleaf and mixed forests stretching from southeastern Canada down through the eastern United States. Their native range covers a wide swath: northeastern states, the south-central and southeastern U.S., and north-central regions where oak, hickory, and walnut trees provide their primary food sources. Five recognized subspecies occupy slightly different portions of this range, from the Carolinas and Georgia up through Pennsylvania and into parts of western Canada where suitable forest habitat exists.
The oldest known fossil of the genus Sciurus dates to the middle-to-late Miocene epoch, roughly 10 to 14 million years ago, found in the Truckee Formation of Nevada. So while today’s gray squirrels are strongly associated with eastern forests, their deeper evolutionary lineage has roots in western North America.
How They Reached the UK
Gray squirrels were imported to Britain starting in the 1890s, brought over from North America as novelties for country estates. The single biggest offender was Herbrand Russell, the 11th Duke of Bedford, who released and gifted gray squirrels from his estate at Woburn Park to locations across the country. Russell was actually a well-regarded conservationist involved in several successful wildlife recovery projects, which makes his role in spreading an invasive species particularly ironic. He also released populations into Regent’s Park, likely seeding the gray squirrel explosion across London.
Research from Imperial College London found that the invasion had far more to do with repeated, deliberate human releases than with the squirrels simply being good colonizers. Multiple wealthy landowners introduced separate populations at different sites, giving the species numerous footholds from which to spread.
Introductions to Italy and South Africa
Italy holds the distinction of being the only country in continental Europe with established gray squirrel populations, and the story starts with just four animals. In 1948, two pairs were imported from Washington, D.C. and released at Stupinigi, near Turin in northwestern Italy. A second introduction followed in 1966, when five squirrels from Norfolk, Virginia were released into the park of Villa Groppallo in Genoa. A third release happened as recently as 1994, when a municipality funded the release of three pairs in the province of Novara. From those tiny founding populations, gray squirrels have spread steadily through the region, raising concern that they could eventually expand across continental Europe.
In South Africa, the introduction traces to Cecil Rhodes, the British colonial figure. Around 1900, Rhodes imported gray squirrels from England to roam the grounds of his Groote Schuur estate in Cape Town. The choice was oddly inconsistent with his well-known passion for English culture, since gray squirrels are North American, not British. Regardless, the population took hold and persists in the Cape Town area today.
Why People Moved Squirrels Around
The Victorian and Edwardian fascination with releasing gray squirrels wasn’t random. It was part of a broader cultural movement that saw urban nature as essential to public health and well-being. In the United States, small-scale releases into city parks were intended to “beautify and add interest” to green spaces. This dovetailed with the parks movement led by Frederick Law Olmsted, which held that nature in cities was critical for maintaining people’s health and providing leisure for workers who couldn’t leave the city.
Squirrels became symbols of something larger. Feeding them was promoted as a way to teach children kindness, both toward animals and other people. Ernest Thompson Seton, cofounder of the Boy Scouts, was among those who endorsed squirrel feeding as a way to “cure children of their tendency toward cruelty.” The fact that squirrels readily approached humans and thrived in busy urban environments made them seem like living proof that extending generosity beyond the human world paid off. That sentimental attachment helps explain why so many people went to the trouble of shipping squirrels across oceans.
Why They Thrive in New Environments
Gray squirrels reproduce quickly enough to establish populations from remarkably small founding groups. Females can produce two litters per year when food is plentiful, with an average of about three young per summer litter and two to three in winter. Litter sizes range from one to six. That reproductive rate, combined with their adaptability to parks, gardens, and fragmented woodlands, means even a handful of released animals can build a viable population within a few years.
They’re also generalist foragers. While they prefer acorns and other tree nuts, they readily eat seeds, fungi, fruit, bird eggs, and the contents of backyard feeders. This dietary flexibility lets them exploit habitats that wouldn’t support more specialized species.
Impact on Native Red Squirrels
Wherever gray squirrels have established in Europe, native red squirrel populations have declined sharply. The mechanism isn’t simply competition for food, though grays do outcompete reds for resources in broadleaf forests. The more devastating factor is a virus called squirrelpox. Gray squirrels carry the virus as a mild, subclinical infection that rarely makes them sick. They function as a natural reservoir for it. Red squirrels, with no evolutionary exposure to the pathogen, develop severe ulceration and crusted lesions around the eyes, lips, feet, and genitalia. The infection is almost always fatal in reds.
This combination of competitive advantage and disease transmission has made gray squirrels one of the most damaging invasive species in Europe. In Italy, where gray populations continue expanding, conservationists worry the pattern could repeat across the continent as the squirrels reach forested corridors connecting to neighboring countries. The story of the gray squirrel is, at its core, a story about well-meaning human decisions creating ecological consequences that are now extraordinarily difficult to reverse.