Articles Features & Opinion

Invasive non-native species (UK) – Grey squirrel

grey squirrel non-native invasive

This week, Elizabeth Kimber (Ecologist), focuses her invasive non-native species article on the grey squirrel…

The grey squirrel (Sciurus carolinensis) is native to North America and was first released into the UK in 1876 by the Victorians. Grey squirrels were introduced in various places around the country and within 25 years, they had colonised 300 miles between Argyll and Stirlingshire in Scotland.

grey squirrel non-native invasive

Identification & Ecology
Identification features of the grey squirrel include grey colour, short front legs and a long bushy tail. Compared to the red squirrel (Sciurus vulgaris), the tail is larger and sturdier, the squirrel is generally larger than the red squirrel. The belly fur on the grey squirrel is always white.

Grey squirrels are present in most woodlands, particularly mature deciduous woods; however, they are also present in open habitats where trees are present. They will readily cross open habitat as long as there are standard trees, but will not often cross open water. Red squirrels appear to be able to compete with grey squirrels in coniferous woodland.

Grey squirrels outcompete the native red squirrel and are highly invasive due to their prolific breeding cycle – if food is available, female grey squirrels can have two litters of young per year. There are usually three young in each litter, which are born in a dray that the mother has built. Eradication programmes for grey squirrels rarely work as neighbouring populations of grey squirrel will fill the habitat availability left by the eradicated squirrels.

Another reason grey squirrels have been more successful than red squirrels is because grey squirrels carry squirrel pox (Parapox virus). This can be carried and spread by grey squirrels and kills red squirrels – the grey squirrel appears to be immune to the disease.

Grey squirrels also impact woodlands by stripping bark off the trees, so they can feed on the soft inner layers. The trees can suffer severe damage from this, or possibly even die, depending on the level of damage caused.

grey squirrel non-native invasive

Legislation which attempts to control the distribution of grey squirrels includes Schedule 9 of the Wildlife and Countryside Act, 1981 (as amended), which makes it illegal to distribute or allow the release of grey squirrels into the wild.

Control Measures
Habitat management can be used to discourage grey squirrels, however, due to the prolific nature of the grey squirrel and the volume of habitat the grey squirrel is present within, it is unlikely that any one method of control will successfully eradicate grey squirrels.

Management aims to improve the habitat for red squirrels to enable them to colonise an area before the grey squirrels establish their colony. However, this is not possible in a lot of the UK anymore.

Where red squirrels are present, management aims to improve and maintain the habitat for this species to ensure the continued survival of the population of red squirrels.


  • Non-Native Species Secretariat – HERE.
  • Woodlands Blog – HERE.

About the Author: Elizabeth Kimber works for an ecological consultancy based in Dorset (Lindsay Carrington Ecological Services Ltd). As part of the role she manages the ecological works for a multi-phase development. She conducts protected species surveys and holds a class 1 bat licence, smooth snake and sand lizard licence. She can be contacted via email: liz (at)