A Firefly's Twinkle Doubles as a Warning Sign to Predators

A group of fireflies twinkling on a summer's night may look peaceful, but those flashing lights can send an unsettling message: 'If you eat me, you'll regret it.' That's what a team of researchers discovered when conducting a study published in Science Advances.

According to the new research, reported by ScienceNews, a firefly's flashing behind acts as a warning signal to predators like big brown bats. Entomologists have long known that fireflies use their lights to attract mates, but the suspicion that they also use them to avoid becoming dinner wasn't confirmed until recently.

To investigate this theory, a team of scientists from Boise State University and other institutions exposed fireflies to three bats with no experience hunting the insects. Fireflies contain toxic chemicals that make them unappealing to predators. After tasting a few of the bugs and spitting them out, the bats learned to stop going after them altogether.

To see what part light played in these interactions, the researcher conducted a separate experiment. They attached tiny paper belts to each firefly and painted them with two coats of black paint—a process that took about 45 minutes for each specimen. The result was a cloak that effectively hid the fireflies' light show. When bats were set loose on the snuffed-out group, it took the predators about twice the amount of time to realize the fireflies were toxic and ignore them. With no visual warning signs to tip the bats off, the study authors suspect that the bats eventually learned to identify the insects from their flight patterns via echolocation.

Fireflies don't light up only when they see a bat swooping their way: Males each have their own "flash fingerprints" they use to attract mates, and females blink in response when they see a display they like. The new study suggests that predators' reaction to this bioluminescent adaptation may have influenced its evolution.