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Fireflies Twinkle to Let Bats Know They Taste Like Garbage

La Crosse, WI, United States / Classic Rock 100.1
Fireflies Twinkle to Let Bats Know They Taste Like Garbage

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SOURCE:  Washington Post

A biologist was studying bats in the tropics a few years ago and observed that the air was full of glowing, slow-flying insects. Jesse M. Barber was puzzled: How could an animal, which makes no evasive maneuvers of any sort, flash lights that ostensibly say “come eat me” still manage to thrive in a forest full of bats?

Barber, a biologist at Boise State University, knew that, although summery constellations of biochemical light are beautiful, fireflies do not flash for our pleasure. The insects cram a lot of information into their blinks — messages of life, death and reproduction. Along with his colleagues, Barber found evidence that firefly flashes contain more than a dating profile. It’s part warning, too: Don’t mess with this beetle.

The typical nocturnal insect goes out of its way to avoid a bat’s notice. Researchers in Barber’s lab call bats “sky wolves,” and though it’s a running joke, it is not far from reality. When providing milk to their pups, female little brown bats can eat their body weight in insects nightly, which means gobbling thousands of bugs.

These ferocious hunters exert an “incredible selective pressure on their prey,” Barber said. Insect species that can’t avoid or defend against bats are not long for this world.

In a study published Wednesday in the journal Science Advances, Barber and his colleagues introduced common eastern fireflies — Photinus pyralis — to a small group of big brown bats.

The researchers assumed that their bats had never seen a firefly before. “These bats are from the western United States, where there are essentially no fireflies,” Barber said. The only fireflies in that region do not produce light as adults.

The bats and fireflies coexisted in a dark room for one to four days. Each bat grabbed a firefly on the first day, then promptly spit it out. High-speed video cameras showed the bats eating scarab beetles and moths, but not fireflies.

The bats loathed the taste of fireflies. Barber said he’d never “seen a stronger negative reaction” to a chemically defended insect. The bats “salivate a bunch and they cough and shake their head and just generally completely despise us for giving them that prey.”

Fireflies might look like harmless nuggets of light, but they’re actually quite toxic. Study co-author Marc A. Branham, who studies insect behavior at the University of Florida, knows this because he experienced their “totally gnarly” taste firsthand.

“I had found a new species and was trying to catch as many species as I could in my net,” he said, when they began escape. Needing a bug-size enclosure, he held a few in his lips and mouth. The beetles were bitter, somewhat acidic, and Branham suspects they would have been even more noxious had he chewed. “As it was, my throat started constricting and my lips went numb.”

After the first taste, the bats didn’t try to eat the fireflies again. They associated the blinking lights with a disgusting meal, researchers concluded.

That firefly light is a warning to predators — don’t eat me, I’m gross — is not a new hypothesis. All fireflies glow as immature larvae — these young beetles cannot mate, ruling out worm-light as courtship ritual. Writing about adult fireflies in the late 1800s, entomologist George H. Bowles speculated, “May not the light then serve … as a warning of their offensiveness to creatures that would devour them?”

But this is the first direct experimental evidence to show that bats avoid the beetles, the study authors said. It turns out that the bats used not one but two signals: auditory and visual signs. “This is, to my knowledge, the first work to show that a three-dimensional flight pattern is information that bats can associate with bad taste,” Barber said.

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