There are two red squirrel species in the northern hemisphere. North American red squirrels are small, and have a red-brown back, a black side stripe, and white belly. Eurasian red squirrels are large with a red to grey grizzled coat and white belly, or are melanistic (black).
The grey squirrel also is large and is a well-known invasive species. Grey squirrels are either a grey-brown grizzled colour with a light belly or melanistic. The squirrel species can also differ in bone and tooth structure, but these features are difficult to examine on live animals.
Answered by Dr Gavin Hanke, curator of Vertebrate Zoology
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