The grey squirrel was introduced to England, Scotland and Ireland from North America in the Victorian era. It has colonised 90% of England and Wales and has expanded from its initial sites in Scotland.
In Britain it has few natural predators and has successfully adapted to British lowland conditions. It is omnivorous, breeds strongly and is an aggressive settler, equally at home in urban parks and the countryside.
Grey squirrels are vectors (carriers) of the squirrelpox virus for which no vaccine is presently available. The virus is deadly to red squirrels but does not affect the host. This is cited as an “example of how diseases carried by invading species can act as biological weapons and speed up their conquest of native species.”
The threat to the economy
It is estimate that grey squirrels have cost the British economy £14 million per annum according to a study published by the international scientific organisation CABI for DEFRA, Scottish Government and the Welsh Assembly – The Economic Cost of Invasive Non-Native Species on Great Britain.
The threat in Europe
The future spread of the grey squirrel into France, Switzerland and eventually other neighbouring countries would pose a significant future problem for commercial forestry, biodiversity and a threat to native wildlife such as the European red squirrel.
The grey squirrel is now posing a serious threat to the great forests of northern Italy, France, Switzerland and Germany.
The threat to flora and fauna
Grey squirrels are identified as having a wide range of impacts from reduction in wood production to an adverse effect on biodiversity.
The grey squirrel (Sciurus carolinensis) is the principal threat to the survival of the red squirrel in Britain. The grey squirrel has already driven out the British red squirrel (Sciurus vulgaris) from all but a few "last outposts" on the mainland.
The grey squirrel has also: