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Stay Out of the Limelight

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Stay Out of the Limelight

Published on July 26, 2016

Firefly by Terry Priest
Common Eastern Firefly (Photinus pyralis) Photo by Terry Priest

East of the Rocky Mountains the summer nights are a sight to see. As the sun sets and the sky grows dark, a show is about to start. Flash. The black of the night is broken as a speck of green light flickers on and off again. Another flash and the air fills with the dancing starlight of fireflies. Lighting up like a neon sign the fireflies practically call out for insect loving bats to come take a bite. So why don’t they?

According to a 2009 study in the Journal of Animal Behavior fireflies have plenty of predators, including other fireflies, but bats aren’t one of them. In the study, both captive and wild bats were shown to steer clear of these light-up snacks rather than swoop in for an easy meal. In fact, the research showed that fireflies aren’t just off the menu, they are so bad that bats won’t even eat delicious meal worms if firefly residue is involved.

What’s going on is pretty clever on the firefly’s part. Advertising yourself with a light up beacon may be good for finding potential mates, but everyone else can see you too. This is where the fireflies’ natural defenses comes in as these crafty insects have a secret chemical weapon ready for anyone who tries to take a bite.

This adaptation comes in the form of a nasty chemical defense inside the firefly that makes them taste pretty bad to predators. No one wants to go through the extra effort of catching a snack that doesn’t taste any good, so rather than waste their energy bats choose hunt for moths, beetles, and other insects. With this trick up their sleeves the fireflies can light up the night as much as they like without having to worry about hungry bats.

Firefly artcile bat
Townsend's big-eared bat (Corynorhinus townsendii)
Photo by Michael Durham

But it doesn’t stop there, not only are the fireflies chemically defended, this study also found that their light show actually acts as a warning. When a firefly lights up it’s not only calling to other fireflies it is also sending a message to the bats saying “Hey! You don’t want to eat me.” And the bats hear them loud and clear. When the researchers looked at four different species of North American bats, including the northern long-eared bat (Myotis septentrionalis), the little brown bat (Myotis lucifugus), and the big brown bat (Eptesicus fuscus), they found plenty of other insects in their diets, but no fireflies.

With chemical defenses and warning sign these little light up bugs can fly safe all summer while the bats know to look somewhere else for a snack. So go outside and enjoy the fireflies, the bats won’t be eating the show any time soon.






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