Researchers in Taiwan have observed sheet web spiders (Psechrus clavis) capturing fireflies and leaving them glowing in their webs for up to an hour. This unusual tactic turns the fireflies’ mating signals into a deadly lure, with other insects attracted to the light before becoming trapped themselves.
Keen to find out more about the hunting strategy, scientists from Tunghai University devised a field experiment in the Xitou Nature Education Area – a mountainous forest park in the heart of the country.
Here, under the cover of darkness, they placed LEDs designed to mimic firefly light in some spider webs, while leaving other webs empty as controls.
The results, published in the Journal of Animal Ecology, show that webs with lights attracted three times more prey than unlit webs, and in the case of fireflies specifically, capture rates increased tenfold.
“Our findings highlight a previously undocumented interaction where firefly signals, intended for sexual communication, are also beneficial to spiders,” explains Dr I-Min Tso, lead author of the study.
“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.”
The study also revealed that most of the glowing fireflies caught in webs were males, likely mistaking the bioluminescence of trapped individuals for potential mates.
Video footage captured during the research shows spiders treating prey differently: moths were eaten immediately, while fireflies were left alive, continuing to emit their mating signals.
“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,” says Dr Tso.
“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 behaviour accordingly.”
Unlike anglerfish and other predators that invest energy in producing their own lures, the sheet web spider appears to save energy by outsourcing this function to its prey.
The researchers suggest this adaptation may have evolved as a cost-effective strategy for survival in subtropical forests of East Asia, where both the spider and its main prey, the winter firefly (Diaphanes lampyroides), are found.
The study notes that although the LED mimics were a close match to real fireflies, future experiments using live insects would provide stronger evidence of this remarkable strategy.
Top image: fireflies in Taiwanese forest. Credit: Getty
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