A nocturnal spider in the East Asian subtropical forests has created an unusual hunting strategy.
This cunning predator is a nocturnal sheet web spider, Psechrus clavis, which captures fireflies as prey.
Rather than immediately consuming captured fireflies, the spider leaves them in its web to continue emitting their bioluminescent light.
This light, which the fireflies use to attract mates, acts as a lure for other prey.
Researchers in Taiwan documented this rare case of a predator exploiting its prey’s mating signal to its own advantage.
“Our findings highlight a previously undocumented interaction where firefly signals, intended for sexual communication, are also beneficial to spiders,” said Dr I-Min Tso, the study’s lead author.
“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 author added.
LED light experiment
The nocturnal sheet web spider is a sit-and-wait predator. Its primary food source is the winter firefly (Diaphanes lampyroides), which attracts mates with a continuous, non-flashing light.
The team experimented using LED lights to mimic the fireflies’ glow in real spider webs. Other webs were left untouched to act as a control group.
Surprisingly, the webs adorned with these artificial lures attracted three times the prey. This number jumped to ten times more when they only counted the fireflies caught.
The study confirmed that spiders that use captured fireflies as bait are much more successful at hunting.
Most of the fireflies caught were male, likely drawn in by the glow they mistook for a mate.
Researchers believe this strategy allows the spiders to “outsource” prey attraction, avoiding the need to develop their own bioluminescence, similar to other night predators like anglerfish.
Differentiating prey
The experiment also revealed that the spiders use different strategies for handling various types of prey.
For instance, when a moth was caught in the web, the spiders would immediately consume it. However, if a firefly were captured, the spiders would not eat it immediately.
This suggests the spiders can distinguish between different species and adjust their behavior accordingly.
“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,” explained 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 behavior accordingly,” Tso added in the press release.
The researchers conducted a field experiment in a conifer plantation forest at the Xitou Nature Educational Area of National Taiwan University.
They noted a limitation in their methodology: they used LEDs to imitate the light of fireflies.
While the wavelength and intensity of the LEDs closely matched those of the fireflies, the researchers acknowledge that using real fireflies would have been ideal for the experiment. However, they admitted that doing so would have been practically impossible.
The findings were published in the British Ecological Society’s Journal of Animal Ecology.