Grey squirrel: Sciurus carolinensis

Distribution: Native to North America. Introduced to Great Britain, Ireland and South Africa.

Habitat: Prefers mature deciduous woodland but also common in parks and gardens in towns and cities.

Description: Winter fur is dense and silvery grey with a brown tinge along the middle of the back. Summer fur is yellowish-brown. White underparts. Bushy, grey tail. Ears without tufts.

The grey squirrel was introduced to Great Britain in the mid-19th century and after many releases it began to increase dramatically at the beginning of this century, mainly spreading from Woburn Park, Bedfordshire. It is now one of Britain’s most well-known and frequently seen mammals, being much more common than the native red squirrel.

Size: Head and body about 25 – 30cm; tail about 20 – 25cm. Weight: 350-600g.

Life-span: Some live up to 10 years in the wild although most only manage 3-4 years.

Food: Hazelnuts, acorns, beech mast, tree bark, fungi, buds, leaves, shoots, flowers; will also raid birds’ nests for eggs and young.

Daily Life

The grey squirrel is diurnal and most active at dawn and dusk, searching for available food. Compared with the red squirrel, it spends more time foraging and feeding on the ground than in the trees. It is, however, very agile in the trees and can run along slender twigs, leaping from tree to tree. The long, muscular hind legs and short front legs help it to leap. The hind feet, longer than the front, are double-jointed to help the squirrel scramble head first up and down the tree trunk. Sharp claws are useful for gripping bark and the tail helps the squirrel to balance. If a squirrel should fall, it can land safely from heights of about 9m (30ft). They grey squirrel can leap more than 6 metres!

Squirrels have good eyesight and often sit upright on a vantage point to look around them. They have a keen sense of smell too!

The grey squirrel builds itself a nest, or drey, about the size of a football, made of twigs, often with the leaves still attached. It is built fairly high in a tree and lined with dry grass, shredded bark, moss and feathers. A summer drey is usually quite flimsy and lodged among small branches. Sometimes the squirrel may make its nest in a hollow trunk or take over a rook’s nest, constructing a roof for it. A squirrel may build several dreys.

Although grey squirrels have a wide range of calls, they communicate mainly through their tails, using them as a signalling device; they twitch their tails if they are uneasy or suspicious. Regular routes are scent-marked with urine and glandular secretions. Squirrels identify each other, and food, by smell.

Winter: The grey squirrel does not hibernate and it cannot store enough energy to survive for long periods without food. A larger, thicker winter drey is built, usually on a strong branch close to the trunk, and a squirrel will lie up in this in very cold weather, coming out now and then to search out hidden stores of food. These stores of single nuts and other items are buried in the ground in autumn, well spread out. They are found by smell, rather than memory. Often they are not found at all and later may grow, helping the dispersal of trees. Winter dreys are often shared for warmth. As it sleeps, the squirrel curls its tail around its body to act as a blanket.


In late winter, squirrels may be seen courting, one, or more, chattering males chasing a female through the tree or across the ground. Females can mate only twice a year, but males may mate at any time. After mating, the male plays no part in the rearing of his young.

The female uses a winter drey as a maternity nest, or builds a new one. She lines it with soft material and gives birth after a six week gestation period (time between mating and birth), in March/April and perhaps again in June/July.

An average litter has 3 babies but as many as 9 may be born. The mother suckles the naked, blind young every three or four hours for several weeks. They gradually grow fur, their eyes open and at about seven weeks old they follow their mother out on to the branches. Gradually they start to eat solid food and when their teeth are fully grown, at 10 weeks, they give up suckling. A month or so later they move away from the nest to build dreys of their own. If there are not too many squirrels in the area, the young stay nearby; if it is crowded they will be chased away to look for less crowded feeding areas.

Grey squirrels breed for the first time at a year old.

Grey Squirrels and humans

Humans are the main predators of grey squirrels in Britain. Foresters, gamekeepers, park keepers and many conservationists regard grey squirrels as pests, mainly because they damage trees. Young saplings are destroyed and they gnaw the bark of hardwood trees, such as beech and sycamore, to get at the nutritious sapwood below. The raw scar left on the trunk encourages fungal attack and may lead to distorted growth.

In many forest areas, the grey squirrel population is controlled by trapping and shooting. Gamekeepers shoot the squirrels on private estates. The Forestry Commission and National Trust also trap and shoot grey squirrels. It is illegal to keep, import and release grey squirrels in Britain, unless you have a special licence from the Ministry of Agriculture or Secretary of State for Scotland.

Although the grey squirrel is a pretty, appealing and entertaining little animal, it can be a great nuisance in a garden, especially to a bird lover. It is very bold and soon learns to take food from bird tables and chew through baskets of peanuts. It will also destroy birds’ nests to eat eggs and nestlings.

Grey squirrels seem much stronger and more adaptable than our native red squirrels and have taken over many of its former territories.  This is partly because grey squirrels carry the squirrelpox virus, to which they are immune, but which affects red squirrels.  Also, their larger size makes them the obvious winners in any physical confrontation with red squirrels.

Black Rats

Also know as the Ship rat or Roof rat. Again, this animal is nocturnal as with the other species of pest rodents. It can be found worldwide but distribution in the UK is very limited and is normally restricted to areas around large ports. It is a major pest of ships. This rat was responsible for spreading (via fleas) the Bubonic Plague throughout Europe in the Middle Ages. Fortunately in the UK, this disease does not exist, but can still be found, to some degree, in many other countries around the world.

Brown Rat

Also known as the Norway rat, Common rat or Sewer rat. It is a worldwide pest of industrial, commercial and domestic premises. It can be a major pest on some farms, where warmth, food and a source of water are easily found. Like the House mouse, this animal is nocturnal, but the Brown rat is very wary of new objects and is said to be neophobic (fear new things). A single Brown rat may produce up to 40 droppings in 24 hours so the contamination potential of these animals is high.

Brown rats are capable of carrying several diseases, amongst which, in the UK, are Salmonella food poisoning and Weils disease (Ieptospiral jaundice).

House Mouse

The House mouse is a worldwide pest of buildings. They are nocturnal creatures and are extremely inquisitive, exploring their surroundings mainly by touch as their eyesight is not particularly good.

A mouse can produce up to 80 droppings in 24 hours, so food and food reparation surfaces can easily become contaminated even when only a small number of mice are present. Probably the most important disease that can be transmitted by mice in the UK is Salmonella food poisoning.