Twirling Tails: How Luna Moths Avoid Predators

 

When you look at this picture of a luna moth, you might think about how beautiful those long pastel green tails are. However, moths use their 'tails' for a more practical, and unexpected, purpose than beauty: fending off predators. They do not directly fight predators, but use the tails to refract the sound waves emitted by bats. How does this work? Bats find their prey by echolocation, or by emitting rapid, high-pitched pings. They bounce off of prey such as moths or mosquitoes, and the bats are able to interpret these refractions and locate the prey. When a luna moth flies, its tails flap and twirl. When bats send out their sound waves, they do not bounce off of the moth itself but off its spiraling tails. Since bats rely almost entirely on sound waves to locate prey, and receive refraction signals from the tails, they attack the tails instead of the moth. These tails tear off easily, and leave the moth unharmed. Sometimes, the confused bats even miss altogether.

 In lab experiments, bats headed for the tails 55% of the time, proving that attacking the tails is not a mere coincidence. Researchers also tested cases where they trimmed the tails off luna moths, and found they were nine times more likely to be caught by a bat. In addition, scientists investigated other possible purposes of long tails in moths, and found that there was no other possible purpose - they were not involved in courtship, and did not assist flight. In fact, long spatulate tails have evolved independently in four different species of moths in the family Saturniidae, further supporting that these tails developed to confuse bats. In another experiment, the survival rate of luna moths was compared to that of a larger, tailless moth. Bats were able to catch the larger moths 66% of the time, showing that luna moths are harder to catch, probably because of their tails. “Clearly, tails provide an anti-bat advantage beyond increased size alone,” Jesse Barber of Boise State University wrote.

Here is a link to a video showing bats missing luna moths because of their flapping tails, followed by a poem I wrote about this phenomenon:

      The Tail of the Luna Moth

A bat emits a stream of high-pitched titters

Sound waves ripple back as a luna moth flutters

Long green tails flap and twitch and twirl

The night is silent save for the crickets’ chorus

As the bat zooms closer to its unwitting target.

No thoughts of predators echo through the moth’s primitive brain

And the bat flits closer with its high-pitched blips

Bouncing off the luna moth’s swinging tails

They hypnotize the bat like a pendulum

They smack the sound waves like a tennis racquet

And they echo back to the bat, refracted

The bat receives the waves’ message

It makes a sharp swoop for its dinner

It does not crunch into the moth’s fat white thorax

It only tears off a tail

As the luna moth spirals and swirls off like a ballerina

Leaving the confused bat with a mouthful of wing scales.

Link to Video: https://www.youtube.com/watch?v=qUiGEWpxqeg#