‘Ballista’ spider builds catapult web that flings ants at 130G

Sydney: A newly discovered spider in Queensland builds a spring-loaded silk trap so powerful it launches its prey into the air with a force that would kill a human.

Researchers from Macquarie University have identified a nocturnal spider in the genus Propostira that targets only one species: the green tree ant (Oecophylla smaragdina). They’ve nicknamed it the “ballista spider” after the Roman crossbow-like weapon.

The trap works like a snare. Shortly after dusk the spider spends up to 4 hours building a cone-shaped web, setting 15 to 60 tightly bunched tension lines attached to a leaf. It then applies a chemical that specifically triggers green tree ants to bite the cone with their mandibles.

When an ant does, the stored elastic energy releases instantly. High-speed cameras running at 5,000 to 7,000 frames per second recorded accelerations of up to 1,367 metres per second squared — about 130 times the force of gravity.

“To capture the moment, we had to push the cameras to 5000 to 7000 frames per second, which I honestly have never had to do… when I’ve been filming animals,” said Ajay Narendra at Macquarie University.

The ant is flung ballistically into the spider’s web. The researchers, including Pranav Joshi, spent 10 days in early 2023 filming the spiders after the trap was first spotted in 2022 by Greg Anderson of QIMR Berghofer in Brisbane.

Scientists say the mechanism is a rare example of a prey-triggered trap, likely an evolutionary solution for handling dangerous prey. The spiders spend daylight hours hiding under leaves and have not yet been formally named.

The findings highlight extreme specialization in predator-prey relationships and raise questions about how many other spiders use similar ballistic traps.