Ballista Spider’s Aggressive Ant Trap Captured in Queensland Rainforests

At night in Queensland’s rainforests, a predator deploys its traps. It creates silky, spring‑loaded webs, seemingly coating them with a scent that both attracts and provokes its prey, then lies in wait.

When an ant approaches, it becomes aggressive and bites the web, causing the trap to snap and launch the victim into the air toward its hunter.

This hunter is a newly described spider now named the ballista spider, after the ancient Roman crossbow. Its prey is the green tree ant. The springy cone‑shaped web is possibly the first known example of a spider using a prey‑triggered trap, according to a study published in Current Biology.

The discovery began years ago when Gregory Anderson, a co‑author of the study, stumbled upon the spider’s cone‑shaped webs. He shared the find with a small group of researchers who immediately recognized its oddity and urged further investigation, said sensory biologist Ajay Narendra of Macquarie University, who was part of the team.

The researchers trekked to the remote Cape York Peninsula to observe the spiders with high‑speed cameras and infrared lighting, and to collect silk samples. They recorded five such fast‑moving traps on film.

“We spent several nights watching and filming these spiders build their webs and hunt green ants,” Dr. Narendra said. The team filmed at 5,000 frames per second to capture the hunting strategy, noting that the traps launched ants at accelerations exceeding 1,300 m/s².

The spiders target the aggressive, territorial green tree ant. Their cone‑shaped webs mimic the ant’s appearance, featuring a large green abdomen and segmented body. The scientists suspect the webs are coated with pheromones that both attract the ant and provoke its aggressive biting response.

The ant’s bite triggers the spring‑loaded web, catapulting the victim toward the ballista spider.

While many spiders use pheromones to lure prey—such as the bolus spider’s sticky blob‑shaped web that swings at moths drawn by a false female scent—this species uniquely exploits a negative stimulus to provoke a reaction.

“In this paper there’s also olfactory mimicry that mimics something the ant doesn’t like,” commented Andrew Gordus of Johns Hopkins University, who was not involved in the research. “I’ve never heard of that before.”

The ballista spider’s cone‑shaped web differs from the “triangle” and “slingshot” webs of other trapping spiders, which rely on the spider to release tension. Here, the prey itself sets off the trap, making it a novel mechanism.

“There are just so many different spider species” that remain undescribed, noted evolutionary biologist Jessica Garb of the University of Massachusetts Lowell. “This is a really fabulous example of an interesting web that wasn’t really described before.”

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