An invasive species is a non-native organism introduced to a new environment that causes, or is likely to cause, harm to that ecosystem, its economy, or human health. This harm can manifest in various ways, such as outcompeting native species for resources or altering habitats. The question of whether red squirrels are invasive is complex, largely due to common misunderstandings and the existence of distinct species.
Identifying Different Red Squirrel Species
The term “red squirrel” refers to several distinct species globally, often leading to confusion about their ecological status. It is important to differentiate between two prominent species: the European Red Squirrel (Sciurus vulgaris) and the American Red Squirrel (Tamiasciurus hudsonicus). These squirrels inhabit different native geographical ranges, with the European species found across Europe and parts of Asia, and the American species native to North America.
The European Red Squirrel
The European Red Squirrel (Sciurus vulgaris) is native to broadleaf and coniferous forests across Eurasia and is not an invasive species; rather, it is a native inhabitant of these regions. In many parts of its range, particularly the United Kingdom and Ireland, its populations have faced significant declines. This decline is largely attributed to habitat loss and competition from the introduced North American grey squirrel (Sciurus carolinensis). The European Red Squirrel plays a role in seed dispersal within its native woodlands, contributing to forest regeneration. While categorized as “Least Concern” globally by the IUCN, its status in the UK is “Near Threatened,” highlighting localized threats to this indigenous species.
The American Red Squirrel
The American Red Squirrel (Tamiasciurus hudsonicus) is native to North America, widely distributed across forested areas of Canada and the United States, commonly found in coniferous, mixed, and deciduous woodlands. Within its native range, the American Red Squirrel is not considered an invasive species. These squirrels are known for their territorial behavior and caching large quantities of conifer cones and other food items in centralized middens. Their diet primarily consists of conifer seeds, nuts, and fungi, and they play a role in seed dispersal. It is typically smaller than the grey squirrel and can be distinguished by its reddish fur and a white ring around its eyes.
Why the Confusion About Invasiveness
The widespread misconception that red squirrels are invasive primarily stems from the well-documented ecological impact of the North American Grey Squirrel (Sciurus carolinensis) in Europe. Grey squirrels were introduced to Europe, particularly the United Kingdom, Ireland, and Italy, from the late 19th century onwards, leading to a dramatic decline in native European Red Squirrel populations. The grey squirrel outcompetes the European red squirrel for food and habitat, being larger, more robust, and able to digest unripe acorns, which red squirrels cannot efficiently utilize, giving them a competitive advantage. Furthermore, grey squirrels often carry the squirrelpox virus, which typically does not harm them but is often fatal to European red squirrels, causing severe symptoms like skin lesions and rapid decline. The presence of this virus can accelerate the decline of red squirrel populations significantly, making the North American grey squirrel classified as an invasive alien species in Europe, while the European red squirrel is the species being negatively impacted.