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A ballista spider (Propostira sp.) waits for a green tree ant (Oecophylla smaragdina) to bite the cone of its web and thus spring the snare. Credit: Professor Ajay Narendra et al
An international team of researchers has discovered a remarkable new spider species in the rainforest of North Queensland that spins an ingenious and powerful spring-actuated snare to catch a single species of ant—one ant at a time—in what they describe as "the ultimate specialization."
Nicknamed the ballista spider after the ancient Roman weapon that used a spring to launch a bolt or stone, the small nocturnal spider has apparently evolved a unique web mechanism to trap only the highly territorial and aggressive green tree ant Oecophylla smaragdina.
A detailed description of the spider's predatory strategy and mechanics is published in the latest issue of the journal Current Biology. The spider—which has yet to be formally named but belongs to the genus Propostira—was first observed by Professor Greg Anderson, a biomedical research scientist who is also a spider taxonomist and photographer.
Lead researcher Professor Ajay Narendra of Macquarie University and postgraduate student Pranav Joshi then spent 10 days and nights in rainforest near Cooktown in far north Queensland, locating the spiders, observing them in detail and capturing their behavior using high-speed and infrared cameras.
Credit: Current Biology (2026). DOI: 10.1016/j.cub.2026.04.066
A trap built for one ant
"It's very unusual for a spider to feed on ants because they're notoriously dangerous, and even more bizarre to find a spider that eats only one particular ant species," said Professor Narendra. "Ants have a range of chemical defenses—including the ability to sting in some species—and they use alarm signals to rapidly recruit hundreds and even thousands of other ants as backup to overcome potential predators."
During the day, the ballista spider takes refuge on the underside of a leaf above an area where green tree ants are actively foraging. As night falls, the spider descends 50 centimeters or more (20 inches or more) to lay an anchor point on a leaf, a branch or the forest floor, then spends up to four hours engineering a vertical arrangement of 15–60 silk tension lines bundled together in a cone near the ground.
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