Grey squirrel
The grey squirrel (Sciurus carolinensis) is considered a woodland pest due to the damage they cause to trees. Learn more about their impact on trees, your management options and how to control their access to individual trees.
Area
The grey squirrel is a non-native species first introduced to the UK from North America in 1876. The UK grey squirrel population was estimated at 2.7 million animals in 2018, according to Natural England’s Joint Publication JP025. The species is widely distributed across most of England, Wales, Northern Ireland, and the Scottish Lowlands.
Status
Unlike the red squirrel, the grey squirrel is not a protected species.
Types of treescapes where this mammal is typically found, along with the level of presence in different treescapes:
- upland broadleaved woodland (frequently found)
- lowland broadleaved woodland (most common)
- mixed plantation (common)
- conifer (frequently found)
- wood pasture, parkland and orchards (common)
Grey squirrels are known for their negative impact on native red squirrels, through:
- direct competition for food
- displacement from preferred habitat
- the spread of squirrel pox virus, a disease that is fatal to red squirrels but not to greys
While grey squirrels do prey on the eggs and nestlings of native birds, current evidence suggests that nest predation by grey squirrels occurs at rates too low to cause population declines in known prey species.
Grey squirrels may serve as important prey for pine martens and Eurasian goshawks, in areas where the species’ ranges overlap.
The tree species most susceptible to grey squirrel damage include:
- sycamore or maple
- beech
- oak
- lodgepole pine
- Norway spruce
- Scots pine
Grey squirrels primarily damage trees through bark stripping. This can:
- occur anywhere from the base of the tree to the canopy
- create structural defects that degrade the tree’s quality
- increase the trees susceptibility to rot and disease
- kill the tree in severe cases
Trees between 10 and 50 years of age are most vulnerable to bark stripping. Grey squirrels may also damage young spruce and larch trees by biting off buds and shoots.
The economic impact of grey squirrel damage is significant. A 2021 Royal Forestry Society Joint Report estimated that grey squirrel damage in England and Wales could cost at least £1.1 billion over the next 40 years.
Widespread use
Lethal control: shooting, trapping.
Occasional use
Enhance natural predation: nest (or den) boxes.
In trial or development
Enhance natural predation: reintroduction or range expansion of predator species.
Non-lethal control: immunocontraception.
Any control must be conducted in line with animal welfare legislation such as the Wild Mammals (Protection) Act 1996 and the Animal Welfare Act 2006. Lethal traps (i.e. permitted spring traps) should not be used when protected species are known to be present in the locality. This particularly applies where red squirrel, pine marten and dormice are concerned.
Widespread use (or strong supporting evidence)
Adapting planting pattern and choice: landscape placement of new woods.
Case studies, trials, and scientific research
Royal Forestry Society
Analysis of the cost of grey squirrel damage to woodland.
Support, advice, and guidance
UK Squirrel Accord
A partnership of 45 signatories working together to protect the United Kingdom’s red squirrels and broadleaf trees from the negative impacts of grey squirrels: UK Squirrel Accord website.
European Squirrel Initiative
Advice and guidance on how to promote the survival of the red squirrel throughout Europe through the control of the grey squirrel: European Squirrel Initiative website.
Forestry Commission
A useful guide to distinguishing squirrel damage from that of other common mammals of English woodlands Forestry Commission grey squirrel guide.
Forest Research
Nearest neighbour method for quantifying wildlife damage to trees in woodland: Forest Research website.
The National Forest
Grey squirrel activity and impact assessment documents: The National Forest website.