The 'ballista spider' builds a trap to catapult unsuspecting prey into its web

A recently discovered spider species in Australia’s tropical rainforests has stunned researchers with a hunting technique that launches prey through the air using a spring-loaded silk trap.

A study, published this week in the journal Current Biology, describes how the tiny arachnid builds a cone-shaped snare to catapult green tree ants into its web, earning it the nickname “ballista spider,” a nod to the ancient Roman weaponry used to launch heavy projectiles.

“To be able to see the behaviour was absolutely breathtaking,” Ajay Narendra, a biology professor at Australia's Macquarie University and one of the study’s lead researchers, told As It Happens host Nil Kӧksal.

The spider belongs to the Propostira genus, and has not yet received a formal species name.

Researcher Greg Anderson first observed the spider in 2022 when he witnessed a green tree ant suddenly fly through the air and get trapped in a web in a remote rainforest on Queensland’s Cape York Peninsula.

The observation prompted a team from Macquarie University to travel from Sydney to northern Queensland to investigate in 2023.

“To be able to even find the spider was a needle in several haystacks,” Narendra said.

Using high-speed cameras, the team spent 10 days documenting the spiders' unusual hunting strategy. The first attack they witnessed happened so quickly they failed to record it.

“By the time we blinked, the ant was caught in the web, so we had no idea what actually happened,” Narendra said. “Lucky for us, nature and behaviours are quite repeatable.”

The spiders are three to five millimetres long, and active exclusively at night. They spend their days hiding under leaves, and once the sun sets they spend up to four hours constructing an elaborate trap beneath their main web.

To set their traps, they descend roughly half a metre and attach between 15 and 60 silk tension lines to a lower anchor point, such as a leaf, branch or the forest floor, according to the study. Those lines are bundled into a taught cone-shaped structure, then wrapped in finer silk.

Green tree ants then bite the cone and become stuck. As the ant struggles, the trap eventually detaches from its anchor point, releasing the stored tension and launching the insect nearly 30 centimetres into the air.

The ant lands directly in the spider's main web, where the predator is waiting.

The green tree ants were attracted to the trap within one minute of this final silk layer being placed, leading researchers to believe this silk may use pheromones to lure these ants, specifically.

“As soon as it builds up that type of silk, it attracts only the green tree ants and no other ants,” Narendra said.

“We went and released a whole bunch of different ants, which were also found on the tree at night on the same tree, and they just ignored it. They didn’t care about it, which was fascinating."

Narendra suspects this hands-off approach is an evolutionary tactic to hunt green tree ants —which are “extremely formidable creatures” and have “strength in numbers" — without ever coming into contact with them.

The team plans to further study the spider silk to identify which pheromones, if any, are used in the prey specialization.

Saad Bhamla, an associate professor at the University of Colorado-Boulder's BioFrontiers Institute, says there could be a “much simpler answer” to how the spiders target their prey.

“What if this ant is already so aggressive and territorial that as soon as a spider builds something in their vicinity, [green tree ants] are out there cleaning up?” said Bhamla, who was not involved in the study.

“Anything is possible, but maybe these ants are just very vigilant compared to the other ants they tested.”

The launch occurs in about 42 milliseconds, and subjects the ants to nearly 15 times the G-force experienced by jet pilots, Narendra says.

That's even more force than what's generated by the slingshot spider, an unrelated species that uses a very similar hunting tactic.

Bhamla, who has researched slingshot spiders, says their strategy is more active because they use their web to launch themselves at flying insects, rather than the other way around.

“It clearly has an upward limit because the more lines it adds, the more force it has to hold with its own legs,” Bhamla said.

The ballista spider does not face the same constraint. Instead, it stores energy in its silk trap, allowing it to launch prey with remarkable force while remaining safely out of reach.

“I think it’s amazing that it’s 2026 and we are still uncovering cool things about nature,” Bhamla said. “We still have so much left to discover.”