Red Squirrels are small charismatic native mammals which depend on a woodland habitat to live, eat and breed. Grey squirrels are non-native and were introduced into Ireland at the beginning of the 20th century (see below).

In 1911 a pair of grey squirrels is believed to have been given as a gift to a resident of Longford Castle, Co. Longford, from where they quickly escaped. When the greys arrive into an area of woodland the resident red squirrels usually disappear within 5 to 15 years. No one is sure exactly how this happens but it is believed that the grey can out-compete the reds in accessing food and as a result the reds starve and become unable to gain enough weight to successfully breed. The grey squirrels  act as a carrier of the pox virus. See Squirrel Pox Virus page.