Fireflies rely on flashing signals to communicate with other fireflies using luminous lanterns on their bellies. In fireflies of the species Abscondita terminalisMales make multi-pulse flashes with two lanterns to attract females, while females make single-pulse flashes with their one lantern to attract males. Now researchers report in the journal Current biology on August 19, we have evidence that an orb-weaving spider (Araneus ventricosus) manipulates the flash signals of male fireflies entangled in its web so that they mimic the typical flashes of a female firefly, luring other males to serve as their next meal.
“We propose this based on extensive field observations Araneus ventricosus uses deceptive interspecific communication by first entangling male fireflies in its web and then predisposing the captured male fireflies to emit bioluminescent signals that differ from those that attract females typically produced by A. terminalis males and instead mimic the male-attracting signals typically made by females,” the researchers wrote. ‘The result is that the captured male fireflies emit false signals that attract more male fireflies to the web.’
The discovery came after the new study’s first author, Xinhua Fu, from Huazhong Agricultural University in China, noticed several male fireflies entangled in the webs of orb-weaving spiders while in the field. Strangely enough, he rarely, if ever, saw a female firefly in a web. Later trips also revealed a similarly lopsided pattern.
This led Fu to suspect that the spiders might attract males to their web by somehow manipulating their flashing behavior. To test this hypothesis, behavioral ecologists Daiqin Li and Shichang Zhang of Hubei University, together with Fu, conducted field experiments that allowed them to observe both the spider’s behavior and the fireflies’ signals. Their research showed that the spider web caught male fireflies more often when the spider was present than when the spider was absent from the web.
Upon further analysis, they found that the signals of male fireflies in webs with spiders were much more similar to the signals of free females. More specifically, the captive males used single-pulse signals using only one of their lanterns, and not both. These captured male fireflies rarely attracted other males when alone in the web.
The findings suggested that the males did not change their flashes as a distress signal. The researchers propose that the spiders alter the firefly’s signal.
“Although the eyes of orb-web spiders typically support limited spatial acuity, they rely more on temporal acuity than spatial acuity for distinguishing flash signals,” Li said. “Upon detecting the bioluminescent signals of ensnared male fireflies, the spider employs a specialized prey handling procedure that requires repeated wrap-bite attacks.”
The findings show that animals can use indirect but dynamic cues to target an exceptionally specific category of prey in nature. The researchers further suggest that there are many more undescribed examples in nature in which predators can use mimicry to manipulate the behavior of their prey, based on communicative signals such as sound, pheromones or other means. They note that more research is needed to find out whether the spider’s venom or the bite itself leads to changes in the flash pattern of the captured males.
This work was supported by the National Natural Science Foundation of China, the National Key R&D Program of China, the Academic Research Fund of the Ministry of Education of Singapore and the Slovenian Research and Innovation Agency.
