These Spiders Use Captured Fireflies as Flashing Lures to Snare More Prey

Some spiders might use captured fireflies as beacons to lure more of the insects into their webs.

In a study of orb-weaver spiders in China, researchers noticed that male fireflies tangled in spiderwebs emitted unusual pulses of light—their flashes mimicked the signals female fireflies make to attract mates. When a spider was present, its web captured more male fireflies, suggesting the predators might influence the insects to change their flashing patterns to draw in more prey, the team reported Monday in the journal Current Biology.

“What a cool behavior,” Ximena Nelson, an animal behaviorist at the University of Canterbury in New Zealand who did not contribute to the findings, says to Science News’ Erin Garcia de Jesús.

“The idea that a spider can manipulate the signaling of a prey species is very intriguing,” Dinesh Rao, a spider biologist at the University of Veracruz in Mexico, tells the New York Times’ Darren Incorvaia. “They show clearly that a trapped firefly in the web attracts more fireflies,” adds Rao, who was not involved in the work but peer-reviewed the research.

Male fireflies of the species Abscondita terminalis attract females by making a series of pulses with the two lanterns on their abdomens. Females, on the other hand, appeal to males with single pulses from their one lantern.

Xinhua Fu, a researcher at Huazhong Agricultural University in China, noticed that orb-weaver spiders often captured male fireflies in their webs, but they rarely snagged female fireflies, according to a statement. To find out why, Fu and his team studied 161 webs in various field experiments.

The researchers captured male fireflies with nets and placed them on the spiderwebs with tweezers. In some of the webs, they used ink to black out the lanterns of the fireflies, while in others, they let them flash. They tested webs when spiders were present, as well as when they were not.

Webs with both a spider and a firefly making visible signals captured significantly more additional fireflies compared to other webs. They outperformed webs without a spider present, webs in which the firefly’s signal was blocked and webs with no fireflies or spider.

Male fireflies made signals that resembled those of females only in the presence of a spider. The findings suggest the spiders may somehow be manipulating the fireflies’ signals to make them appear female, thus drawing more male fireflies into the web.

The spiders also treated fireflies and non-flashing beetles differently. The predators lightly wrapped fireflies so their lanterns remained visible, while they wrapped other beetles in a thicker layer of silk, Daiqin Li, a co-author of the study and animal behavior expert at Hubei University in China, says to Science News. They began to feed on the other beetles almost as soon as they were caught, but they left fireflies in the web, presumably to act as decoys.

“[The findings] once again demonstrate that spiders are not passive foragers,” Mariella Herberstein, a behavior ecologist at Macquarie University in Australia who did not contribute to the findings, tells New Scientist’s Jake Buehler. “We are discovering more and more cases of highly complex and selective feeding techniques.”

More research is needed to determine what exactly prompts the male fireflies to flash like females—it could be the spider’s venom or the act of biting the prey, the study authors write. Li tells the New York Times that the venom is the more likely culprit. “Spiders didn’t bite the lantern directly,” Li says to the publication. “Perhaps the spider’s venom disrupts normal flashing behavior by interfering with the delivery of oxygen supply.”

Still, some researchers aren’t yet convinced that it’s actually the spider that’s manipulating the flashing.

“It appears something is altering the signals, but the evidence provided in this study isn’t enough to identify what specifically is causing the changes,” Kathryn M. Nagel, who studies spider behavior at the University of California, Berkeley, and did not contribute to the findings, writes in an email to National Geographic’s Gennaro Tomma. “Further research is needed to determine if the spider’s actions … are directly manipulating the signaling behavior.”

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.