The red squirrel or Eurasian red squirrel (Sciurus vulgaris) is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of tree squirrel

Tree squirrel

Tree squirrels include over a hundred species that are found on all continents except Antarctica, and are the members of the squirrel family most commonly referred to as "squirrels"...

 in the genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Sciurus

Sciurus

The genus Sciurus contains most of the common, bushy-tailed squirrels in North America, Europe, temperate Asia, Central America and South America.-Species:There are 30 species.Genus Sciurus - Tree squirrels*Subgenus Sciurus...

 common throughout Eurasia

Eurasia

Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

. The red squirrel is an arboreal

Arboreal locomotion

Arboreal locomotion is the locomotion of animals in trees. In every habitat in which trees are present, animals have evolved to move in them. Some animals may only scale trees occasionally, while others are exclusively arboreal. These habitats pose numerous mechanical challenges to animals...

, omnivorous

Omnivore

Omnivores are species that eat both plants and animals as their primary food source...

 rodent

Rodent

Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....

.

In Great Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

 and Ireland

Ireland

Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

, numbers have decreased drastically in recent years, in part because of the introduction of the eastern grey squirrel

Eastern Gray Squirrel

The eastern gray squirrel is a tree squirrel in the genus Sciurus native to the eastern and midwestern United States, and to the southerly portions of the eastern provinces of Canada...

 (Sciurus carolinensis) from North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

.
The red squirrel has a typical head-and-body length of 19 to 23 cm (7.5 to 9 in), a tail length of 15 to 20 cm (5.9 to 7.9 in) and a mass of 250 to 340 g (8.8 to 12 oz).