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.