The three species of New World flying squirrels, genus Glaucomys, are the only species of flying squirrel found in North America. They are distributed from Alaska to Honduras. They are similar in many ways to the Eurasian flying squirrels in the genus Pteromys. Two species of New World flying squirrels can be easily distinguished on the basis of size and ventral pelage. Northern flying squirrels, Glaucomys sabrinus are larger and have belly hair that is dark at the base and white at the tip. Southern flying squirrels, Glaucomys volans, are smaller and have belly hairs that are completely white. Humboldt's flying squirrel is more difficult to distinguish from the northern flying squirrel where their ranges overlap. In fact, they were once considered conspecific. Humboldt's flying squirrel is considered a cryptic species. They are generally smaller and darker than northern flying squirrels.