There are two species of flying squirrels in the state – the common southern flying squirrel (Glaucomysvolans) found throughout much of the state and the Special Concern northern flying squirrel (Glaucomys sabrinus) restricted to the northern third of Wisconsin. The nocturnal flying squirrels can be distinguished from tree squirrels by presence of extremely large eyes, flattened tail, and a furry patagium (loose flap of skin allowing for gliding).
Flying Squirrel Info:
https://dnr.wi.gov/files/PDF/pubs/er/ER0678.pdf
Flying Squirrel FAQ:
https://widnr.widen.net/s/lqdg6tbbzb/flying-squirrel-faq_final