Not content to rely on pure happenstance, the spider, Araneus ventricosus, has found a way to hack the firefly’s bioluminescent signals to lure more fireflies to its web, new research has found.
It does this by making captive male fireflies emulate 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 exactly how the spider manages this feat.
“The spider manipulates the flashing signals of male fireflies ensnared in its web to mimic the typical flashes of a female firefly, thereby luring other males searching for mates,” said study author Daiqin Li, a behavioral ecologist at Hubei University in China.
Female fireflies are usually stationary, Li explained, so only male fireflies tend to get trapped in — and are more likely to be lured to — spider webs.
Fu also noticed some of those male fireflies were making female flashing signals at that time.
“Each trial lasted for 2 hours, providing ample time to observe and record the interactions and behaviors.” Their experiments showed that the spiders’ webs captured male fireflies more often when the spider was present than when the spider was absent.
“The precise mechanisms by which the spider alters male firefly bioluminescent behavior 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 added.
Every evening at dusk, a common species of orb-weaving spider constructs new webs in the paddy fields and around ponds in central China. This allows it to trap fireflies that start to flash, flicker, and glow at the same time.
Araneus ventricosus, a spider, has discovered a method to manipulate fireflies’ bioluminescent signals in order to attract more of them to its web. This is because the spider is not satisfied to rely solely on coincidence.
It achieves this, according to a study published on Monday in the journal Current Biology, by forcing captive male fireflies to mimic the single-pulse mating signals of female fireflies. Exactly how the spider accomplishes this is still unknown.
“The spider mimics the typical flashes of a female firefly by manipulating the flashing signals of male fireflies entangled in its web, thus attracting other males seeking mates,” explained Daiqin Li, the study’s author and behavioral ecologist at Hubei University in China.
According to Li, male fireflies are more likely to be drawn to and become entangled in spider webs than female fireflies because the latter are typically immobile.
Web discoveries.
The firefly breeding season, which typically lasts two weeks from mid-May to mid-June and is when they are most active, increases the likelihood that a firefly will be consumed by a spider. The lanterns, which are microscopic organs that release light via a biochemical process, are located on the abdomens of the glowing insects.
The new research focuses on the species of fireflies called Abscondita terminalis. The males of this species use two lanterns to create multi-pulse flash patterns to attract females, while the sedentary females use one lantern to create single-pulse signals.
Twenty years ago, study coauthor Xinhua Fu, a specialist in fireflies at Huazhong Agricultural University in China, noticed male-only firefly clusters on the webs of orb-weaving spiders. Fu also saw that some of those male fireflies were flashing like females at that moment.
Li, Fu, and associates made the decision to carry out experiments involving 161 webs in order to conduct additional research. The researchers found and measured webs every evening during the firefly mating season on farmland in a village near Wuhan. They divided the webs into four groups and recorded temperature, relative humidity, and other variables.
They captured male fireflies using a net, and depending on the variables they were examining, they used a pen to blacken some of the fireflies’ lanterns to prevent them from flashing. Next, they used tweezers to place the fireflies on the webs and, in some cases, remove spiders.
A video camera captured the reactions of free-flying male fireflies that were later trapped by the webs in four distinct scenarios, each with two variables: whether or not a spider was present in the web and whether or not the captive male fireflies that the researchers added to the webs were flashing signals resembling those of females due to blacked-out lanterns.
“We counted the number of additional fireflies that were ensnared by each web every 5 to 10 minutes during the tests,” Li wrote in an email. Every trial had a two-hour duration, which gave plenty of time to watch and document the behaviors and interactions. “.
Their research revealed that when the spider was present, its webs caught male fireflies more frequently than when it wasn’t. Additionally, they verified that the signals produced by male fireflies in webs containing spiders resembled those of female fireflies considerably more: the captured males used only one lantern, rather than both, as would be expected, to emit single-pulse signals.
Theories on firefly signal deception.
As per the study, it was observed that the male fireflies were not changing their flashes as a distress signal. This was because there were significantly more free-flying fireflies entangled in the webs with a spider than when there was none at all, indicating that the change in behavior wasn’t due to the fireflies getting entangled in the web.
After observing that the spiders bite the firefly repeatedly after spotting the male on its web, the researchers surmise that the spiders modify the firefly’s signal in some way. It’s unclear, though, if the males who are ensnared would change in their pattern of flashing due to the bite or the venom of the spider.
According to Li, “the precise mechanisms by which the spider modifies male firefly bioluminescent behavior remain unexamined.”.
“Male fireflies in particular frequently resumed their regular multi-pulse flashing pattern when we removed them from the web and gave them a brief recuperation period,” he continued. “Maybe the venom of the spider interferes with the regular flashing behavior. “.
Although not involved in the study, Dinesh Rao, principal investigator at the Rao Spider Lab at Universidad Veracruzana in Mexico, concurred that the venom of the spider may be the source of its ability to control the firefly’s light show. He continued, describing the behavior of the spider as “surprising” but not wholly unique, pointing out that certain bolas spider species attract male moths by creating substances that resemble the pheromones of female moths.
Rao wrote in an email, “This is a very interesting case of manipulation of a visual signal.”. It is still unclear, nevertheless, what mechanism underlies the alteration in flashing behavior. “.
