The gray squirrel, Sciurus carolinensis, an adaptable and rapidly proliferating rodent, presents significant challenges in regions where it is not a native species. Their presence can lead to a range of environmental and economic issues, particularly through competition with native wildlife and damage to forestry and human property.
Threat to Native Wildlife
Gray squirrels pose a substantial threat to native wildlife, particularly the Eurasian red squirrel (Sciurus vulgaris), through competition and disease. Gray squirrels are more adaptable and efficient at exploiting food sources. This competitive advantage leads to reduced body growth in young red squirrels, affecting their reproduction and survival.
Beyond direct competition, gray squirrels are carriers of the squirrelpox virus (SQPV), to which they are immune but which is often fatal to red squirrels. The mortality rate for infected red squirrels can be as high as 100%, with death typically occurring within two weeks. The virus can spread through direct contact with infected lesions or contaminated materials, such as feeders. When SQPV is present, gray squirrels can replace red squirrel populations at a significantly faster rate, sometimes 20 to 25 times quicker than through competition alone.
Ecological and Forestry Damage
Gray squirrels inflict considerable damage on woodland ecosystems, primarily through bark stripping. This occurs when squirrels remove sections of bark from trees to access the nutrient-rich phloem layer beneath. Trees most vulnerable to this damage are often young broadleaf species.
Bark stripping stresses and weakens trees, making them susceptible to pests and pathogens, and can ultimately lead to tree mortality. If the stripping encircles the trunk or branch, it can effectively “ring-bark” the tree, causing it to die. This damage degrades timber value through staining and structural defects. The economic impact of gray squirrel damage to trees is estimated to be at least £37 million annually.
The ecological consequences extend to hindering woodland regeneration and altering forest composition. Extensive bark stripping can prevent young trees from maturing, leading to a loss of future large trees that support diverse ecosystems. This widespread damage can disincentivize the planting of native broadleaf species, potentially leading to a long-term decline in native woodlands.
Property and Garden Disruption
In urban and suburban environments, gray squirrels frequently cause disruption to property and gardens. Their continuously growing incisors necessitate constant gnawing, which can lead them to chew on electrical wires, wooden structures, and insulation. This gnawing on wiring poses a fire hazard by exposing live electrical currents and causing short circuits.
Squirrels often gain access to attics and sheds, where they can damage insulation and other building materials. Homeowners may hear scurrying sounds in walls or attics, indicating their presence. Beyond structural damage, squirrels are notorious for raiding bird feeders, consuming large quantities of birdseed and often damaging the feeders themselves.
In gardens, gray squirrels can be destructive, digging up newly planted bulbs and corms. They also consume fruits, vegetables, and flower buds, and can damage lawns while burying or retrieving food caches. This behavior can lead to significant losses for gardeners and require protective measures like wire mesh or fencing to safeguard plants.