Scientists at Tunghai University, Taiwan, now have evidence of spiders using the bioluminescent light emitted by captured fireflies to attract additional prey. While some bioluminescent predators use their own light to attract prey, the researchers behind the discovery say this is a rare example of predators using the mating behavior of another species to their advantage.
According to a statement detailing the unusual arachnid behavior, some sit-and-wait predators such as anglerfish use bioluminescence to attract prey. However, the team’s new findings are the first documented evidence of sheet web spiders (Psechrus clavis) using the bioluminescence of another species to their predatory advantage.
Found in the subtropical forests of East Asia, the species are nocturnal hunters that dine primarily on the winter firefly (Diaphanes lampyroides). Like most firefly species, the winter firefly emits light flashes to attract a mate.
When the team collected video evidence of the spiders’ nighttime activities, they said they were not surprised to see them immediately kill and consume trapped moths and other insects. They were, however, surprised to witness the spiders leaving trapped fireflies untouched for up to an hour until they had stopped emitting light. The team even witnessed the spiders checking on the fireflies from time to time, potentially to see if they were still giving off light.
Dr. I-Min Tso, the lead author of the study detailing the unexpected behavior, said the discovery of spiders handling separate prey differently suggests they may use a “cue” to determine which type of potential meal is trapped in their web. The researcher also speculated that the spiders may be able to detect the firefly’s bioluminescence, “enabling spiders to adjust their prey handling behavior accordingly.”
To determine how effective the trapped firefly hunting strategy was, the Tunghai University team conducted a field experiment in the conifer plantation forest at National Taiwan University’s Xitou Nature Educational Area.
First, the team located genuine sheet spider webs. Next, they placed smaller LEDs disguised as fireflies in half of the webs while leaving the others untouched as study controls. Although the team set up the wavelength and intensity of the LEDs to closely match the mating signals from fireflies, they concede the experimental results would be more accurate using real fireflies as bait, noting that “this would be very difficult in practice.”
As hoped, the team immediately saw that more potential prey were attracted to the trapped LED “fireflies” than to the control group web. Further analysis revealed that three times as many unfortunate creatures were attracted to the LED-equipped webs as to the untreated ones. When the team examined the number of fireflies trapped in the LED-equipped webs exclusively, they found that the ratio was ten times that of the control group. The team also found that most of the attracted fireflies were male, indicating they were “likely mistaking the glow for potential mates.”
Dr. Tso said their experiments confirm that captured fireflies left as bait can significantly increase the hunting success rate of sheet web spiders. The researcher also noted that their findings “highlight a previously undocumented interaction” where bioluminescent firefly signals, intended for communicating mating availability, “are also beneficial to spiders.”
“This study sheds new light on the ways that nocturnal sit-and-wait predators can rise to the challenges of attracting prey and provides a unique perspective on the complexity of predator-prey interactions,” Dr. Tso added.
The research “Prey bioluminescence-mediated visual luring in a sit and wait predator” was published in the British Ecological Society’s Journal of Animal Ecology.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.