Red squirrels spend the majority of their foraging time in the tree canopy, whereas greys feed more frequently on the ground. Reds can be distinguished from greys by their long ear tufts and fur colour, although grey squirrels can be a brown-red colour in the summer, and reds sometimes taking on a greyish hue in the winter, leading to some confusion. Red squirrels are distinctly smaller, weighing approximately half that of a grey squirrel. The establishment and subsequent spread of this alien species has resulted in competition with the red squirrel for food resources, with the red squirrel invariably losing out to the grey. The second squirrel species is the American grey squirrel ( Sciurus carolinensis) that was introduced on just one occasion in 1911 to Co. The current population mainly derives from reintroductions that took place in a number of locations during the 19th century.

It is totally dependent on woodland as a habitat, and through deforestation has suffered a number of troughs, including almost complete extinction in the 17th century. There are two species of squirrel currently in Ireland. The red squirrel ( Sciurus vulgaris) is a native species that has been present since before the last ice age.