Ballista Spider: The Catapult‑Like Carnivore of Australian Rainforests

A unique hunting strategy has been revealed by scientists in the remote rainforests of northern Australia. The ballista spider, a diminutive member of the genus Propostira, constructs a spring‑loaded silk trap that specifically targets a single prey species – the aggressive green tree ant (Oecophylla smaragdina).

During the night, the spider descends about 50 centimetres to a leaf or branch, anchors a silk line, and builds an antenna‑shaped scaffold of tension lines. A thin outer silk envelops the structure, preparing it to spring in response to the ant’s touch.

When an ant latches onto the trap, the spider’s build triggers a release, launching the ant into a secondary web with an acceleration described as 15 times the g‑forces experienced by jet pilots. This catapult mechanism allows the spider to safely transport predatory ants away from the nest, reducing risk of retaliation.

Macquarie University researchers spent ten nights in Queensland’s tropical forests, filming the spider’s behavior with high‑speed and infrared cameras. The team found that only green ants were captured by the trap, suggesting the spider may apply specific pheromones to entice this species.

Professor Ajay Narendra noted that the ballista’s snare is a highly specialised tool evolved to remove a hazardous prey one at a time. Dr Jonas Wolff emphasised that, unlike most spiders, this arachnid’s web is designed for a single prey type and is activated by the prey rather than by the predator.

This discovery is unprecedented, offering new perspectives on spider‑ant relationships and the evolutionary arms race in rainforest ecosystems. The findings, published in the journal Current Biology, highlight the complexity of biological interactions in one of the planet’s most biodiverse habitats.