The aye-aye (Daubentonia madagascariensis) is a type of lemur, a primate found only in Madagascar. It has rodent-like teeth that keep growing all the time and a thin middle finger used to find grubs and larvae inside tree trunks.

It is the world’s largest nocturnal primate. To find food, it taps on trees to locate grubs, then uses its forward-slanting incisors to chew small holes in the wood. It inserts its narrow middle finger into the hole to pull out the grubs. This method of searching for food is called percussive foraging and takes up 5–41% of its time searching for food. Only two other living mammal species, the striped possum and trioks (Dactylopsila), use this method. These animals live in northern Australia and New Guinea and are marsupials. From an ecological perspective, the aye-aye plays a role similar to woodpeckers, as it can break through wood to remove insects inside.

The aye-aye is the only living member of its genus, Daubentonia, and its family, Daubentoniidae. It is classified as Endangered by the IUCN. Another species, Daubentonia robusta, appears to have gone extinct within the last 1,000 years. Evidence of this species comes from subfossil remains found in ancient deposits.

Etymology

The genus Daubentonia was named after the French naturalist Louis-Jean-Marie Daubenton by his student, Étienne Geoffroy Saint-Hilaire, in 1795. At first, Geoffroy thought about using the Greek name Scolecophagus, which means "worm-eater," because of the aye-aye’s eating habits. However, he chose not to use this name because he was unsure about the aye-aye’s behavior and whether other similar species might be found later. In 1863, British zoologist John Edward Gray created the family name Daubentoniidae.

The French naturalist Pierre Sonnerat was the first to use the common name "aye-aye" in 1782 when he described and illustrated the lemur. At the same time, English zoologist George Shaw called it the "long-fingered lemur" in 1800, but this name was not widely used. Sonnerat said the name "aye-aye" meant "a cry of exclamation and astonishment." However, American paleoanthropologist Ian Tattersall wrote in 1982 that the name may be similar to the Malagasy name "hai hai" or "hay hay," which refers to the animal and is used across the island. According to Dunkel et al. (2012), the common use of the Malagasy name suggests it could not have come from Sonnerat. Another idea, proposed by Simons and Meyers (2001), is that the name comes from "heh heh," which means "I don’t know" in Malagasy. If this is true, the name might have been used by Malagasy people to avoid saying the name of an animal they feared or considered magical.

Evolutionary history and taxonomy

The aye-aye’s classification was debated after it was discovered because of its unique physical traits. Its continuously growing front teeth are similar to those of rodents, leading early scientists to incorrectly place it in the rodent group and compare it to squirrels because of its toes, fur color, and tail. However, the aye-aye also shares traits with felines, such as its head shape, eyes, ears, and nostrils.

Classifying the aye-aye within the group Primates has also been unclear. It was once thought to be a highly evolved member of the Indridae family, a group that split early from other primates, and its relationship to other primates was uncertain. In 1931, Anthony and Coupin placed the aye-aye in the group Chiromyiformes, which is closely related to other primates. Colin Groves supported this classification in 2005 because he was unsure whether the aye-aye shared a common ancestor with other lemurs on Madagascar.

However, genetic studies consistently show that the aye-aye is the most ancient type of lemur. The most likely explanation is that all lemurs descended from a single ancestor that traveled from Africa to Madagascar during the Paleogene period. Similarities between the aye-aye’s teeth and fossilized remains of African primates (Plesiopithecus and Propotto) suggest another possibility: that the aye-aye’s ancestors reached Madagascar separately from other lemurs. In 2008, Russell Mittermeier and Colin Groves, among others, avoided discussing higher-level classifications and instead grouped lemurs into five families, including Daubentoniidae.

Evidence that the aye-aye belongs to the group Lemuroidea includes the presence of bony structures called petrosal bullae that protect the ear bones. The aye-aye also shares a trait with lemurs: shorter back legs.

Anatomy and morphology

A full-grown aye-aye is usually about 60 centimeters (2 feet) long, with a tail longer than its body. The species has an average head and body length of 36–43 cm (14–17 in), plus a tail of 56–61 cm (22–24 in), and weighs about 2 kilograms (4 pounds).

Young aye-ayes are often silver-colored on their front and have a stripe along their back. As they grow older, their bodies become fully covered in thick fur, and their fur is not one solid color. The hair on their head and back often ends in white tips, while the rest of their body is usually yellow or brown.

One of the aye-aye’s most unique traits is its fingers. The third finger is much thinner than the others and is used to pull grubs and insects out of trees using a hooked nail. This finger has a special joint that allows it to reach the throat through the nose, which helps the aye-aye eat mucus from inside its nose. The aye-aye also has a sixth digit, called a pseudothumb, which helps it grip objects.

The ridges inside the aye-aye’s ears have a special shape that helps it focus sounds. These ridges work like a type of lens called a Fresnel lens, which helps focus light. This feature is also found in other animals, such as the lesser galago, bat-eared fox, mouse lemur, and others.

Female aye-ayes have two nipples located near their groin. Male aye-ayes have genitalia similar to those of dogs, including a large prostate and a long baculum.

Behaviour and lifestyle

The aye-aye is a nocturnal and tree-dwelling animal, meaning it spends most of its life in trees. While it sometimes comes down to the ground, aye-ayes sleep, eat, move, and mate in trees. They are often found near the top of forests where thick leaves provide protection. During the day, they rest in round nests made of leaves, branches, and vines in the forks of tree branches. At night, they leave their nests to search for food. Aye-ayes are solitary, meaning they live alone, and they mark their large areas with scent. Female aye-ayes often share their territory with one or two males, while male aye-ayes may share their territory with other males. They may even share the same nests, but only at different times. Males seem to tolerate each other until a female calls for a mate.

Aye-ayes can mate any time of the year, and females usually begin breeding at three or four years old. They have one baby every two to three years. While caring for their young, females are the dominant ones, likely to help secure food for their baby. The baby stays in the nest for up to two months before exploring outside, but it takes seven more months to move through the canopy as skillfully as an adult.

The aye-aye is an omnivore, eating seeds, nuts, fruits, nectar, plant sap, fungi, and insects like wood-boring beetle larvae and honey. To find food, aye-ayes tap on tree trunks and branches up to eight times per second, listening for echoes that reveal hollow spaces. Once a hollow is found, they chew a hole in the wood and use their long, bony middle fingers to pull out grubs. Aye-ayes begin foraging about 30 minutes before sunset and continue for up to three hours after sunset. They spend about 80% of the night searching for food in the canopy, with short breaks in between. They move by leaping between branches, similar to squirrels. They rarely jump between trees horizontally and can travel up to 4 kilometers (2.5 miles) each night.

Although foraging is usually done alone, aye-ayes sometimes forage in groups. Members of a group use sounds and scent to coordinate their movements.

Scientists once thought aye-ayes were solitary because they do not groom each other. However, recent studies suggest they are more social than previously believed. Aye-ayes typically stay within their own territory, which is a specific area they claim as their own. Male territories often overlap, and males can be friendly with each other. Female territories never overlap, but a male’s territory may overlap with the territories of several females. Male aye-ayes live in large areas up to 32 hectares (80 acres), while females live in smaller areas up to 8.1 hectares (20 acres). Males find it hard to defend a single female because of their large territory, so they often mate with multiple females. Aye-ayes use scent from their cheeks and neck to mark their territory and warn others to stay away.

Like other prosimians, female aye-ayes are more dominant than males. They are not usually monogamous, meaning they do not stick to one mate. Males compete for mates, and sometimes pull other males away from a female during mating. Mating sessions can last up to an hour, and males and females only interact occasionally outside of mating, usually while foraging. The aye-aye is the only primate known to use echolocation to find prey.

Distribution and habitat

The aye-aye mainly lives on the east coast of Madagascar. Its natural home is rainforests or dry deciduous forests, but many now live in farmed areas because forests are being cut down. Rainforest aye-ayes, which are the most common type, live in the tops of trees and are usually seen above 70 meters high. They sleep during the day in nests made from twigs and leaves twisted together, located high up in the trees among vines and branches.

Conservation

The aye-aye was believed to be extinct in 1933, but it was found again in 1957. In 1966, nine aye-ayes were moved to Nosy Mangabe, an island near Maroantsetra off the eastern coast of Madagascar. Recent studies show that the aye-aye lives in more areas than previously thought, but its conservation status was changed to endangered in 2014. This is due to four main reasons: local cultures believe the aye-aye is evil and kill it for this reason. The forests of Madagascar are shrinking because of deforestation. Farmers sometimes kill aye-ayes to protect their crops, and poaching is also a serious problem. However, there is no clear proof that aye-ayes harm crops, so they are often killed based on superstition.

As many as 50 aye-ayes live in zoos around the world.

The aye-aye is often seen as a sign of bad luck and death and is killed when seen. Some people believe that if an aye-aye points its narrowest finger at someone, that person is marked for death. Others think that if an aye-aye appears in a village, someone in the village will die, and the only way to stop this is to kill the aye-aye. The Sakalava people believe that aye-ayes enter homes through thatched roofs and kill sleeping people by using their middle fingers to stab their main blood vessel.

Conservation efforts for this species have been helped by breeding programs in captivity, especially at the Duke Lemur Center in Durham, North Carolina. This center has been important in caring for, studying, and breeding aye-ayes and other lemurs, including how they grow from babies. It has also helped scientists better understand what aye-ayes eat. Jersey Zoo in the United Kingdom also helps protect the species. After bringing six aye-ayes from the wild in 1990, they achieved the first successful breeding in captivity in 1992. They also keep a global record of the species and manage the European breeding program.