An elephant swinging its tail

An elephant’s pendulum-like tail swings fast enough to create an airy barrier to biting insects. Credit: Marguerite Matherne and David Hu

Biophysics

Why an elephant’s tail is a feeble fly-swatter

Tails serve as effective non-lethal weapons against pests.

A mammal’s waving tail forms a curtain of air that can discourage most mosquitoes from landing — and blows the pests away.

Tail-wagging in mammals such as elephants has long been thought to ward off biting insects, but the behaviour has received little attention from scientists. David Hu and his colleagues at the Georgia Institute of Technology in Atlanta recorded tail swinging in zebras, giraffes, elephants, horses and dogs. The team calculated that although the animals’ tails wagged rapidly, they could strike only one insect every 90 seconds.

Noticing that wind from a swishing tail spurred mosquitoes to take off, the researchers designed a cylinder that included a fan. After mosquitoes were released into the container, the fan's blades spun at the frequency of a specific mammal’s tail swings.

For the tail-swing rate of a wide range of species, the fan generated gusts of air whose speed closely matched that of flying mosquitoes, the authors report. They estimated that the breeze could block 50% of mosquitoes from landing — and those insects that did slip through could be swatted with the mammal’s tail.