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In the paddy fields and around the ponds of central China, a common species of spider weaves a new orb web each evening at sunset, allowing it to absorb fireflies that begin to flash, flicker and burn around the same time. .
Not content to rely on imagination, the spider, Araneus ventricosus, has found a way to hack the firefly’s bioluminescent signals to attract more fireflies to its web, new research has found.
It does this by having captive male fireflies mimic the single-pulse mating signals of female fireflies, according to a study published Monday in the journal Current Biology, although it’s not yet clear how the spider manages the feat. this.
“The spider manipulates the flashing signals of male fireflies encased in its web to mimic the normal flashing of female fireflies, thereby attracting other males looking for mates,” the study author said Daiqin Li, a behavioral ecologist at Hubei University in China.
Female fireflies tend to be stationary, Li explained, so male fireflies tend to get caught in — and more likely to be drawn to — spider webs.
Web reviews
Fireflies are most likely to be on the spider’s menu during the firefly breeding season, usually a two-week period from mid-May to mid-June, when they are particularly active. On their abdomens, the luminous insects have lanterns, tiny organs that emit light through a biochemical reaction.
Male fireflies of the species studied in the new research, Abscondita terminalis, attract females by using two lanterns to make multi-pulse flash patterns, while sedentary females attract males by making single-pulse signals with a single lantern.
Study co-author Xinhua Fu, a firefly expert at Huazhong Agricultural University in China, for the first time male-only clusters of fireflies on the orb weaving spider web 20 years ago. Fu also noticed that some of the male fireflies were flashing female signs at that time.
Li, Fu and their colleagues decided to investigate further by conducting experiments involving 161 webs. During firefly mating season on farmland in a village near the city of Wuhan, the researchers located and measured the webs every evening, dividing the webs into four different groups, and recording temperature, relative humidity and other factors.
With a net, they caught male fireflies and used a pen to blacken some of the fireflies’ lanterns to stop them from flashing, before placing the fireflies on the webs using tweezers and removing spiders in some cases by depending on the variables they were investigating.
What happened to the free-flying male fireflies that were subsequently caught by the webs was observed on video camera in four different situations involving two different variables: whether or not there was a spider in the web and whether the captive male fireflies that the researchers added to the webs by the researchers making. flashing signs like women or not (because their lanterns were blackened).
“During the tests, we monitored each web every 5 to 10 minutes to count the number of additional fireflies ensnared,” Li said in an email. “Each trial lasted 2 hours, which provided plenty of time to observe and record the interactions and behaviors.”
Their experiments showed that spider webs caught the male fireflies more often when the spider was present than when the spider was absent. They also confirmed that the signals made by male fireflies in spider webs looked much more similar to those of female fireflies: the ensnared males emitted single-pulse signals using only one of their lanterns, not as expected.
Firefly signal deception: theories
The results, according to the study, indicate that the men were not changing their flashes as a sign of distress, because the number of free-flying fireflies that were ensnared in the webs containing a spider and flashing male fireflies was much higher than when not. A spider was present, indicating that the change was not the result of being caught in the web.
Based on their observations, the researchers believe that the spiders change the signal of the firefly in some way, probably as a result of repeated bites deployed by the spider when it detects the male firefly on its web. However, it is unclear whether changes in the flashing pattern of the ensnared males were caused by the spider’s venom or the bite itself.
“The precise mechanisms by which the spider alters the bioluminescent behavior of male fireflies remain unexplored,” Li said.
“When we removed (the fireflies) from the web and allowed a short recovery period, the male fireflies often resumed their normal multi-pulse flashing pattern,” he said. “Maybe the spider’s gene interferes with normal lightning behavior.”
Dinesh Rao, principal investigator at the Rao Spider Lab at Universidad Veracruzana in Mexico, who was not involved in the study, agreed that the spider’s ability to manipulate the firefly’s light show may be based on the gene. The spider’s behavior was “surprising” but not entirely new, he said, noting that some species of bolus spiders attracted male moths by producing chemicals that mimic female moth pheromones.
“In this case, there is a manipulation of a visual signal, which is very interesting,” Rao said in an email. “However, the mechanism behind the change in lightning behavior remains to be understood.”
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