Aye-aye at the Vienna Museum of Natural HistoryAn aye-aye is a lemur belonging to the family Daubentoniidae. Aye-ayes live only in Madagascar. They can be found in a variety of habitats, including rainforest, deciduous forest, littoral forest, coconut groves, mangrove swamps and plantations.

Only one species of aye-aye,  Daubentonia madagascariensis, is alive today.

Aye-ayes spend most of their time in treetops. They walk and climb on four limbs.

They are between  14 and 17 inches (36 and 44 centimeters) long, excluding their long, bushy tails, which are more than twice as long as their bodies.  They weigh around 6 pounds (2.7 kilograms) and have long, woolly, grey dark brown or black fur with white flecks, big, yellow-brown eyes and big, hairless, ears that can move independently of each other.

An aye-aye's hands and feet are unique. It has claws on all of its fingers and toes, except for its two big toes, which have nails.

It middle finger is extremely long and bony-looking. The aye-aye uses its long middle finger to locate and squash wood-boring insect larvae, an important part of its diet. The aye-aye searches for hollows in tree branches,  which signify the presence of larvae, by tapping on the branches with its middle finger and listening with its large ears. When the aye-aye find insect  larvae,  it chews through the wood with long, sharp rodent-like front teeth and then crushes the larvae with its middle finger.

The aye-aye will also use its middle finger to scoop out the insides of fruit.

Aye-ayes are particularly partial to coconuts. They also eat fungi, seeds and nectar.

The aye-aye has a third eyelid, or nictitating membrane. This may protect its eyes from debris when it is chewing through wood.

Unlike other primates, the aye-aye has two nipples on its abdomen, rather than on its chest.

Aye-ayes are nocturnal. During the day, they sleep in nests in tree forks.  Although they sleep alone, different aye-ayes may use the same nest at different times.

Solitary animals, aye-aye communicate by leaving scent marks and by vocalizing. Aye-ayes have a number of distinctive calls.

Female aye-ayes reach sexual maturity when they are about 2 ½ years old. They give birth every two or three years and usually have one offspring at a time.

Aye-ayes are critically endangered because of habitat loss, hunting and superstition - some natives of Madagascar believe aye-ayes are evil omens, so they kill the animals when they see them.

For a long time, people thought aye-ayes were extinct; they were rediscovered in the 1950s.

Daubentonia robusta, the giant aye-aye, an extinct species, weighed between 2.5 and 5 times as much as Daubentonia madagascariensis.