Sneaky Orb-Weaver Spiders Use Male Fireflies To Lure More Prey

In the wild, animals frequently use deceptive tactics to survive. For instance, some wasps turn spiders into "zombie" slaves to build intricate nests. Similarly, mouse-eared bats mimic hornet buzzes to avoid being preyed upon by owls. Now, a new study reveals that a crafty orb-weaver spider species has found a way to manipulate the mating signals of male fireflies to catch more prey.

The Araneus ventricosus is a nocturnal orb-weaver spider found primarily in China, Japan, and Korea. They build their webs in the evening. This is the same time fireflies emerge to attract mates, making them easy prey. Female fireflies emit single flashes to attract males, while males use two flashes to attract females.

Xinhua Fu, a researcher at Huazhong Agricultural University in Wuhan, China, was out studying fireflies when he noticed something interesting. The orb-weaver spider webs contained caught many male fireflies but very few females. A closer look revealed that many of the ensnared fireflies were still alive. However, they were emitting a single flash instead of their usual two. It appeared as though they were mimicking female fireflies.

To determine if the altered signal was the reason for the larger number of males, Fu and his team decided to investigate further. They found 161 orb weaver webs and randomly divided them into four experimental groups. The first group had a male firefly on a web with a spider present. The second group had a male firefly but no spider. The third group had both a male firefly and a spider, but the firefly's light was blocked with black ink. The control group had no fireflies or spiders.

The researchers found that most fireflies were trapped by the first group of webs — where both both spiders and male fireflies were present. Notably, the spiders wrapped the fireflies in a light layer of silk. This ensured their flashes remained visible. In contrast, other insects like beetles were covered in a much thicker layer of silk. Male fireflies were also kept alive longer than other prey. However, they only emitted single, female-like signals when a spider was nearby. This suggested that the spiders may be manipulating the fireflies' signals to attract more prey.

“When we removed them from the web and allowed a short recovery period, the male fireflies often resumed their normal multi-pulse flashing pattern,” said study co-author Dr. Li.

The researchers are not sure how the spiders get the fireflies to emit just one flash instead of two. But they suspect it is caused by the spider's venom.

“Spiders didn’t bite the [light-emitting] lantern directly,” Dr. Li said. "Instead they targeted other soft body parts. Perhaps the spider’s venom disrupts normal flashing behavior by interfering with the delivery of oxygen supply."

The scientists revealed their findings in Current Biology on August 19, 2024. They plan to continue their research to uncover more details and search for similar behavior in other animals.

Resources: eurekalert.org, science.org, Livescience.com