Sheet-web spiders Psechrus clavis have been known to use their body color and webs as visual cues to deceptively lure and immediately consume insects. However, they do not immediately consume trapped male fireflies Diaphanes lampyroides; instead, the spiders retain them in their webs while the fireflies continue to emit their bioluminescent signal for up to an hour. According to a team of researchers from Tunghai University, the University of New South Wales, the University of Technology Sydney and the National Museum of Natural Science in Taichung, Taiwan, this observation raises the question: can the spiders exploit prey signals to attract additional prey, thereby enhancing their foraging success?
Sheet web spider with fireflies caught in web. Image credit: Tunghai University Spider.
Tunghai University researcher I-Min Tso and colleagues have observed Psechrus clavis spiders capturing fireflies in their webs and leaving them there while they emitted bioluminescent light for up to an hour.
They even observed the spiders going to check on the captured fireflies from time to time.
Intrigued by this unusual behavior, the study authors set up an experiment to test whether this was a strategy used by the spiders to increase their hunting success.
In the experiment, they placed LEDs that resembled fireflies, in real sheet spider webs and left other webs clear as controls.
They found three times the amount of prey was attracted to webs with the LEDs compared to the control webs.
This increased to ten times more prey when they only looked at fireflies being captured.
The findings confirm that captured fireflies left as bait increase the hunting success rate of the spiders.
The researchers also noticed that the majority of captured fireflies were male, who were likely mistaking the glow for potential mates.
“Our findings highlight a previously undocumented interaction where firefly signals, intended for sexual communication, are also beneficial to spiders,” Dr. Tso said.
“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.”
“This behavior could have developed in sheet web spiders to avoid costly investment in their own bioluminescence like other sit-and-wait predators, such as anglerfish.”
“Instead, the spiders are able to outsource prey attraction to their prey’s own signals.
Video footage captured by the scientists in their experiment shows sheet web spiders employing different strategies when interacting with different prey species.
Spiders would immediately consume any moths captured in their webs but would not immediately consume fireflies they captured.
“Handling prey in different ways suggests that the spider can use some kind of cue to distinguish between the prey species they capture and determine an appropriate response,” Dr. Tso said.
“We speculate that it is probably the bioluminescent signals of the fireflies that are used to identify fireflies enabling spiders to adjust their prey handling behavior accordingly.”
The study was published in the Journal of Animal Ecology.
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Ho Yin Yip et al. Prey bioluminescence-mediated visual luring in a sit and wait predator. Journal of Animal Ecology, published online August 27, 2025; doi: 10.1111/1365-2656.70102