The fireflies are kept inside the webs for as long as they glow, before being consumed.
Nocturnal spiders have been caught on camera using fireflies as living lures, keeping the glowing insects in their webs for up to an hour to attract more prey, according to a recent study.
Researchers observed that when fireflies were present on sheet webs, these spiders captured significantly more prey than when the webs were empty. This suggests the spiders are deliberately exploiting the fireflies’ bioluminescent signals to improve their hunting success.
“Our findings reveal a previously undocumented interaction where firefly signals, intended for mating, also benefit spiders,” said I-Min Tso, a spider behavior researcher at Tunghai University. “It highlights how nocturnal predators can creatively attract prey and demonstrates the complexity of predator-prey interactions.”
The study focused on sheet web spiders (Psechrus clavis), which construct their sheet-like webs near the ground in East Asia’s subtropical forests. The researchers noticed that these spiders often had winter fireflies (Diaphanes lampyroides) caught in their webs and wondered if the glowing insects were being used as visual bait.
To test this, the team ran field experiments with LED lights mimicking fireflies and compared webs with and without lights. They found that LED-lit webs attracted three times more prey than empty webs, and captured 10 times more fireflies than the non-LED controls.
Video footage revealed that while other insects, like moths, were eaten immediately, the fireflies were often left in the web for up to an hour—roughly the same amount of time a female firefly typically emits a steady glow. Most of the captured fireflies were male, possibly mistaking the stationary glow for a potential mate.
Unlike some predators, such as anglerfish, that produce their own bioluminescence, these spiders appear to exploit fireflies’ natural sexual signals to their advantage. “The way spiders handle different prey suggests they can recognize fireflies and adjust their behavior accordingly,” Tso explained. “It’s likely the bioluminescent signals themselves guide the spiders’ response.”