How do aye-ayes use their third finger?
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.