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“What a cool behavior,” says Ximena Nelson, an animal behaviorist at the University of Canterbury in Christchurch, New Zealand, who was not involved with the study. The new observations add a unique hunting tactic to spiders’ repertoires (SN: 9/18/23).
Behavioral ecologist Daiqin Li of Hubei University in Wuhan, China, and colleagues set up cameras on spiders’ webs in nearby farmland to watch what happened to fireflies caught in them. The team placed a firefly directly into the orb weavers’ spider webs and either left the spider or removed it from its web. After each trial started, the researchers counted how many additional fireflies got caught in webs every few minutes.
In the webs of Araneus ventricosus spiders, the fireflies changed their flashes. But in the webs of other spiders, Li says, they did not.
Male fireflies were more likely to get caught in webs and change their flashing pattern when an A. ventricosus orb weaver spider was around compared with when it was absent. Those spiders were also less likely to capture more fireflies when Li and his team painted over the insects’ flashing lanterns with black ink, the team observed.
Trapped males that had been bitten and wrapped in a spider’s silk also stopped using both their lanterns (males have two) to pulse light. Flashing just a single lantern, the males’ signals became weaker, single pulses of light, appearing much closer to a female flashing pattern.
The orb weavers also handled fireflies differently than nonflashing beetle species, Li says. While spiders wrapped other beetles in a thick layer of silk and began to feed almost immediately, fireflies got a light wrapping so their lanterns were still visible and then were stocked away in the web.
As more fireflies get caught, Li says, the spiders “repeat the sequence for each of them and leave them there, just flashing.”
The jury is still out on how exactly the signals change, Nelson says. Li suspects the spider’s bite or venom has something to do with it. He’s now planning to test those ideas and look for orb weavers outside of southeast Asia that use this tactic.