The grey squirrel is non-native. It was introduced into Co. Longford in the early years of the present century and has since spread to a few other counties in the midlands and the north. Like most North American animals it is more robust and aggressive than its European counterpart and often out competes it wherever it is found. However, Grey squirrels prefer hardwoods - particularly mature trees in demesnes and the like - while the Red squirrel is most abundant in softwood plantations.

As with the Red squirrel the Grey constructs dreys, characteristically in the smaller branches and not usually in a major fork in the tree, and leafy twigs are used - unlike the bare ones used by the Red. Three or four young are produced in two litters in early spring and mid-summer and the young stay in the drey until the autumn. Grey squirrels feed on a variety of nuts and seeds from trees. The berries and fruits of shrubs and trees supplement the diet as do fungi and birds' eggs (and nestlings) in season. Despite its opportunistic behaviour the Grey does less damage to conifer plantations than does the Red.

The Grey is much larger (about 18in./50cm) than the Red and is almost twice as heavy (up to 2lb/ 0.75kg). It is generally grey above but the fur is suffused with yellowish-brown in the summer, particularly on the face and back. The tail is less furry but longer than that of the Red and is silvery edged. The underbody fur is white. The facial appearance is more 'rat-like' and less 'cute' than that of the Red. The ears are quite round-ended and not pointed and tufted as in the native species.

It is less 'nippy' than the Red squirrel but it is nonetheless very agile, running up and down tree trunks with equal ease. When sitting upright to eat it often twitches its long tail in a nervous fashion. It moves easily over the ground in a series of fluid hops and will forage for scraps in litter bins and carparks.