So ... Sometimes Fireflies Eat Other Fireflies | Deep Look

Most firefly flashes are pure romance, a sexy form of skywriting. But one variety copies the mating signals of others to lure them to their demise.

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Most of the blinking signals that fireflies send out are intended to attract mates. But researchers are finding out that in some cases, these romantic overtures are not all wine and roses.

Females of one firefly group, the genus Photuris, have learned to copy other fireflies’ flashes to attract the males of those species. When one arrives, she pounces, first sucking his blood, then devouring his insides.

These “femme fatale” fireflies live throughout the Eastern U.S alongside the fireflies they target. They can develop widely varying light shows to target whatever species are in the area.

The predatory habits of Photuris are just one example of how much individual firefly signals can differ from one another.

The male Common Eastern Firefly, for example, is known for his fish hook-shaped aerial maneuver, which he repeats at six-second intervals. That characteristic move has earned the species the nickname “Big Dipper.”

The male Big Dipper hopes this bit of skywriting will get him noticed by females hiding in the grass. If the female likes what she sees, her reply comes as a single pulse from her smaller, heart-shaped lantern. That’s his invitation to land and mate.

Most firefly interactions follow the same pattern, with roving males advertising themselves to concealed females. Within a species, the back-and-forth signals are so reliable that it’s easy to attract the male fireflies with even a simple decoy.

Firefly light is biochemical. But fireflies like the Big Dippers do much more with chemistry than just make light. They can mix together an array of other compounds, including invisible pheromones for mating, and others called lucibufagins (“loosa-BOOF-ajins”) that ward off predators like spiders and birds.

At some point, the Photuris “femme fatale” fireflies lost the ability to make their own lucibufagins. So instead of chemistry, these bigger, stronger fireflies became adept at imitation, and evolved to turn into insect vampires to take these valuable compounds from other fireflies to boost their own defenses.

And it works. In experiments, predators avoided Photuris fireflies that had recently preyed on other fireflies.

--- Where do fireflies live?

There are fireflies worldwide, but in the U.S., you’ll find them in the Midwest and Eastern U.S. There are a few species in the West, including the California Pink Glow-worm.

--- Why do fireflies flash?

Mostly, it’s to attract mates. One sex, usually the male, uses a more elaborate flash pattern to get the attention of the opposite sex. Then the female signals her interest with a simpler flash.

--- Why do fireflies glow after they die?

The chemicals in the firefly that make light, luciferin and luciferase, remain viable after it dies, and the reaction that creates the light thrives on oxygen, which is of course plentiful in the air.

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