A nocturnal spider newly documented in the rainforests of northern Queensland has been found to weave a conical, catapult-like silk snare that launches its sole prey—aggressive green tree ants—upwards into a waiting web. The study, published in Current Biology by researchers from Macquarie University, marks the first recorded instance of a spider’s web being designed to catch a single prey species, with the release mechanism activated by the prey’s own bite rather than by the spider. The tiny arachnid, provisionally nicknamed “ballista” after the ancient missile weapon, belongs to the genus Propostira and has not yet received a formal scientific name.

Over ten nights of infrared and high-speed camera recording, the team observed the spider descending roughly 50 centimetres at dusk to anchor a vertical scaffold of 15 to 60 tensioned silk lines, grouped into a cone near the forest floor. The structure is then wrapped with a finer silk. When a green tree ant (Oecophylla smaragdina) approaches and bites the cone, the tension releases, flinging the ant upward at an acceleration exceeding 1,300 metres per second squared—equivalent to 15 times the extreme g-forces experienced by fighter-jet pilots. The ant lands in the spider’s main web, where it is immobilised and wrapped before being consumed at a safe distance from the ant colony’s trails.

The trap’s exclusivity is striking. Researchers released other nocturnal ant species near the snare, but the spider did not respond. The team suspects the spider applies a pheromone to the silk that specifically provokes aggressive biting by O. smaragdina workers, triggering the mechanism. Viewed from the perspective of evolutionary biology, the adaptation appears to solve a high-risk foraging problem: green tree ants possess chemical defences, can sting, and rapidly summon large numbers of nestmates, making them dangerous prey for most spiders. The spring-loaded trap allows the ballista spider to isolate a single ant and remove it from the colony’s communication range before an alarm is raised.

Analysis of the silk’s elastic properties is ongoing, with early indications that the tension lines store and release energy with exceptional instantaneous power density. The next milestone will be the formal taxonomic description of the species and further biomechanical characterisation of the snare’s silk, which could inform biomimetic materials research. The initial discovery was made by biomedical researcher and spider photographer Greg Anderson, whose field observations prompted the Macquarie-led expedition.