What is the largest nocturnal primate?

The largest nocturnal primate is the aye-aye.

The aye-aye, Daubentonia madagascariensis, is a bizarre-looking lemur found only on Madagascar. It is the world’s largest primate that is primarily active at night. Its shaggy fur, large ears, continuously growing incisors, and unusually long middle finger make it unlike any other living primate.

To find grubs hidden inside wood, the aye-aye taps on branches and listens for hollow spaces. It then gnaws through the bark with rodent-like incisors and uses its narrow middle finger to pull out the larvae. This feeding method is known as percussive foraging and occupies the ecological niche that a woodpecker might fill elsewhere.

People sometimes mistake the tarsier for the largest nocturnal primate because tarsiers are famous for their huge eyes. Tarsiers are much smaller, however. The aye-aye is itself a type of lemur, but its specialized anatomy is so unusual that early European naturalists struggled to classify it.