Which of the following squirrels is nocturnal and native to Pennsylvania?

The Flying Squirrel is indeed nocturnal and native to Pennsylvania, distinguishing it from the other options. Unlike most squirrels, which are diurnal and active during the day, Flying Squirrels are adapted to a nighttime lifestyle. Their large eyes are well-suited for low-light conditions, enabling them to navigate and forage effectively after dark. This nocturnal behavior also helps them avoid predators that are active during the day.

The other species listed, such as the Eastern Gray Squirrel, Fox Squirrel, and Red Squirrel, are primarily active during daylight hours. These species are familiar sights in Pennsylvania's woods and urban areas, often foraging for food during the daytime when they are most active. Their behaviors and adaptations reflect their diurnal lifestyles, which is contrasted sharply by the unique characteristics of the Flying Squirrel.