Tree squirrel

Lore & Background

Tree squirrels are defined by their habitat rather than physiology, living mostly among trees. An exception is the flying squirrel, which also lives in trees but has special flaps of skin called patagia that allow gliding flight. The best-known genus is Sciurus, which includes the eastern gray squirrel of North America (introduced to Great Britain in the 1870s), the red squirrel of Eurasia, and the North American fox squirrel. Many tree squirrel species have adapted to human-altered environments such as rural farms, suburban backyards, and urban parks. Current taxonomy, based on genetic data, splits tree squirrels into several subfamilies: Ratufinae (Asian giant squirrels), Sciurillinae (South American pygmy squirrel), Sciurinae (mostly American tree squirrels), Callosciurinae (Asian tree squirrels), and Xerinae (African tree squirrels). These include genera such as Microsciurus, Rheithrosciurus, Tamiasciurus, Callosciurus, Funambulus, and many others. Tree squirrels have been kept as pets in Western society at least until the 19th century, especially popular with women and the clergy due to their small size and tame nature. They are also considered pests because of their propensity to chew on various objects, their persistence, and their habit of burying food, which can annoy gardeners. They can cause fire hazards by gnawing on electrical insulation, and have been responsible for power outages, including bringing down the NASDAQ stock market twice.

Reader's Guide

Tree squirrels are significant as a widespread and adaptable group of arboreal rodents that have successfully colonized human environments across most of the world. Their importance lies in their dual role as both beloved urban wildlife and persistent pests. They are a common type of urban wildlife, often trained to be hand-fed, and they cache surplus food. However, they cause economic losses to homeowners, nut growers, and forest managers, as well as damage to electric transmission lines. Their gnawing behavior, while necessary for maintaining their continuously growing teeth, leads to property damage and fire hazards when they chew on electrical insulation. Squirrels have even caused major power outages, including twice bringing down the NASDAQ stock market. Despite these issues, they pose almost zero risk of transmitting rabies. Efforts to mitigate conflicts include physical exclusion, repellents like capsaicin, and trapping. The Nutty Narrows Bridge in Longview, Washington, listed on the National Register of Historic Places, provides a way for squirrels to cross a busy street safely, illustrating the ongoing human effort to coexist with these animals.

Did You Know?

• Tree squirrels do not form a single natural, or monophyletic, group; they are variously related to ground squirrels, flying squirrels, marmots, and chipmunks.
• The defining characteristic of tree squirrels is their habitat (living mostly among trees), not their physiology.
• Flying squirrels are an exception: they also live in trees but have special flaps of skin called patagia that allow gliding flight.
• Squirrels have brought down the NASDAQ stock market twice and were responsible for a spate of power outages at the University of Alabama.