Fireflies use their characteristic flashing signals to find and attract mates. It’s a courtship ritual that can seem magical on a warm summer evening. However, for orb weaver spiders, these displays are more than just a spectacle — the spiders can manipulate the light signals of male fireflies, turning them into unwitting lures to attract more prey to the spiders’ web, new research reveals.
Both male and female fireflies of the species Abscondita terminalis emit bioluminescent flashes from their abdomens to attract mates. However, females are typically more sedentary, emitting a single pulse of light from a blade of grass or tree branch. Male fireflies emit two pulses of light as they fly about looking for females. Since males are more active, they are much more likely to be caught in a spider’s web to begin with.
But researchers have found that orb weaver spiders (Araneus ventricosus) are not satisfied with the occasional firefly passerby. To increase their food supply, the spiders manipulate the male fireflies to change the light patterns they emit. Instead of two flashes, once ensnared, male fireflies begin to emit a single pulse of light like a female firefly.
“The outcome is that the entrapped male fireflies broadcast false signals that lure more male fireflies into the web,” the study authors write.
The researchers conducted experiments on 161 orb weaver webs on farmland near Wuhan, China. They created four different treatments: webs with spiders and without spiders, as well as webs with normal fireflies and webs in which the researchers obscured the bioluminescent lanterns on their abdomens.
The researchers found that when male fireflies were ensnared in a web with spiders present, they were more likely to produce the single flash of a female firefly. However, if the spider was not present in the web, the fireflies produced the double flash that is expected from a male firefly. The researchers suggest therefore that the spider itself is somehow able to manipulate the male fireflies into mimicking female fireflies, thus luring other males to their doom. Indeed, when the spiders were present on the web, more male fireflies were caught in the trap.
The exact mechanism for the spider’s deception is uncertain, but the study’s authors hypothesize that the spiders manipulate the fireflies by deploying a series of “wrap bite attacks,” in which the spiders ensnare the fireflies with their silk and bite them to inject venom. More research is, however, needed to better understand if it is the act of biting or the venom that is causing the change in the fireflies, the authors write.
“This study, and others like it, highlight how organisms previously dismissed are capable of complex behavior, and how we still have so much to learn about spider behavior,” Kathryn Nagel, a spider researcher at the University of California, Berkeley, U.S., who was not involved with this research, told National Geographic.
Banner photo: courtesy of Xinhua Fu.
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