As the insect sentinels of summer, fireflies use their glowing bellies to communicate to other fireflies. Males from the species Abscondita terminalis use multi-pulse flashes with both of their lanterns to attract females. The females use single-pulse flashes with their one lantern. However, a new study found that some spiders may have decoded this signal and are using it to its advantage. This mimicry is detailed in a study published August 19 in the journal Current Biology.
When orb-weaving spiders (Araneus ventricosus) trap male fireflies in their webs, they manipulate the flashing signals to mimic the typical flashes made by female fireflies. These feigned flashes then lure other males into the web where they become the spider’s next meal. However, we still don’t know if the spider’s venom or a bite itself is manipulating the firefly’s signal.
[Related: A new theory on why fireflies glow—and why they need help.]
The discovery arose after Xinhua Fu, a study co-author and entomologist at Huazhong Agricultural University in China observed several male fireflies entangled in orb-weaving spider webs while working in the field. He rarely saw a female firefly trapped in a web and additional field trips revealed this sexually skewed pattern. Fu hypothesized that the spiders may be somehow manipulating the fireflies’ behavior to attract others.
To test this hypothesis that the spiders are manipulating the firefly’s signal, he recruited behavioral ecologists Daiqin Li and Shichang Zhang from Hubei University. The team conducted field experiments where they observed the firefly signals and spider behavior. The observations showed that the spider’s web captured male fireflies more often when the spider was there, compared to when it was away from the web.
After further analysis, they found that the signals created by male fireflies in webs with spiders present looked more like the signals made by free flying females. The trapped males used single-pulse signals that use only one lantern and not both.
Interestingly, the ensnared male fireflies very rarely lured other males when they were alone in the web and the spider was not around. This suggests that the males were not altering their flashes as a kind of distress signal. The team believes that the spiders are altering the firefly’s signal.
“While the eyes of orb-web spiders typically support limited spatial acuity, they rely more on temporal acuity rather than spatial acuity for discriminating flash signals,” Li said in a statement. “Upon detecting the bioluminescent signals of ensnared male fireflies, the spider deploys a specialized prey-handling procedure involving repeated wrap-bite attacks.”
[Related: Spider glue might evolve faster than the spiders themselves.]
According to the team, the experiment reveals that some animals are capable of using indirect yet dynamic signaling to go after a very specific category of prey in nature. The team also believes that there could be many other undescribed examples of this kind of mimicry in nature waiting to be uncovered. Predators could be using sound, pheromones, or other means, and not just visual signals to fool their prey. This deceptive ability is not exclusive to the animal kingdom either. The South African daisy appears to trick flies into mating with it and depositing pollen.
“We propose that in response to seeing the ensnared male fireflies’ bioluminescent signals, the spider deployed a specialized-prey handling procedure based on repeated wrap bite attacks,” the team wrote in the study. “We also hypothesize that the male firefly’s neurotransmitters may generate a female-like flashing pattern.”
However, additional study is needed to determine what exactly is changing in the trapped firefly’s flashing pattern.
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