Hair does more than keep animals warm. Although it can trap dirt and other debris, it also keeps the animal clean. A new study in the Journal of Experimental Biology measured the hairs of 27 mammals and insects to get to the root of how hair helps us. 

They found that hair increases the effective surface area of an animal’s body—the surface area of an animal’s hair is 100 times that of its skin. A honeybee, for instance, has a surface area around the size of a slice of bread when you account for its hair. That’s a lot of area to trap dirt particles, but hair is also designed to help move dirt and bacteria away from the animal’s skin.

When a dog (or cat) shakes itself, its hairs act “as springboards to catapult accumulated particles,” the researchers write, flinging dirt away. Bees brush off pollen from their bodies with bristles on their forelegs. Cicadas have hair-like structures on their wings that are sharp and pointy, and use them to impale bacteria. 

The researchers suggest that understanding biological cleaning mechanisms like eyelashes might help engineer better self-cleaning materials.


Image Credit: Amador and Hu, Journal of Experimental Biology (2015)

A bonus fun fact: a honeybee and a squirrel have the same number of hairs, about 3 million. A butterfly has about 10 billion. 

[h/t: The New York Times]