Why do aye-ayes have such long middle fingers?

An aye-aye's third finger is highly distinctive being very long and spindly. The structure of this digit is of particular importance to a specific feeding behaviour known as ‘percussive foraging’, a method of seeking out beetle larvae only recorded in aye-ayes and striped possums.

An individual taps on a length of wood (at a rate of up to eight times per second) and listens for an echo that suggests the presence of a chamber beneath.

If a cavity is detected, the aye-aye uses its specialised teeth to gnaw an entry hole, then inserts its finger to probe for prey, its uniquely designed ball-and-socket joint allowing the necessary rotation and flexibility.

Aye-ayes are the only member of the lemur family to have clawed fingers and toes (apart from the big toe). The claw on the third finger is large and curved, allowing it to hook out the unsuspecting grubs with ease.

However, that’s not the only use for these long fingers. It turns out that aye-ayes also use them to pick their noses! After seeing a captive aye-aye doing this, Prof Anne-Claire Fabre from the University of Bern was inspired to look into why some primates pick their noses.

Main image: Aye-aye on a palm frond, Masoala Peninsula, Madagascar. © Thorsten Negro/Getty