The Curious Case of the Aye-Aye's Middle Finger

The aye-aye, an odd-looking lemur indigenous to Madagascar, has a very unusual extra-long middle finger that it uses to forage for food.

Scientists have discovered that the unusual finger is even more unusual, as the aye-aye can thermoregulate the temperature of that finger by as much as 6C:

When not in use, the finger appeared black on thermal images. This indicated a large difference in temperature between it and the white (hot) ears and eyes.

But when the animal was looking for food, the finger rose in temperature by up to 6C.

"We think the relatively cooler temperatures of the digit when not in use could be related to its [long, thin] form," said Ms Moritz.

"This form results in a relatively high surface-to-volume ratio [but] such a ratio is bad for retaining heat."

In order to sense the vibrations of beetle larvae through the bark of a tree, the finger is "packed with sensitive nerve endings", the scientist explained.

Because of its specialist sense receptors, using this tapping tool is very costly in terms of energy.

"Like any delicate instrument, it is probably best deactivated when not in use," Ms Moritz told BBC Nature.


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