Ballista spider catapults ants with deadly snare

A newly described group of ballista spiders in Australia builds a conical web trap that targets green tree ants and flings them into the air—measured at accelerations up to 1367 m/s², around 130 times gravity—before the ants tumble into the spider’s main web.

On a warm Australian night, a spider can spend hours building a trap that looks almost like a little engineering project: a conical snare made of tightly bunched tension lines. Then it waits.

The moment matters. A green tree ant (Oecophylla smaragdina) bites the cone of the web. the snare springs. and the prey is launched—so violently that researchers have measured accelerations up to 1367 metres per second squared. That’s 130 times the force of gravity, enough that the scientists describe it as lethal to a human.

“This time, we had to push the cameras to 5000 to 7000 frames per second,” says Ajay Narendra at Macquarie University in Sydney, describing the effort required to capture the instant the trap fires. “I honestly have never had to do… when I’ve been filming animals.”

The trap was first seen in fragments in 2022. Greg Anderson at QIMR Berghofer Medical Research Institute in Brisbane. Australia. had witnessed a green tree ant being catapulted in a spider trap in the far north of Queensland. But without the right cameras. he could only make out the movement as a blur—prey lifted ballistically by a strange-looking conical web.

It was only after early 2023 that Narendra and Pranav Joshi. also at Macquarie University. spent 10 days studying and filming these nocturnal spiders. They say the spiders do not yet have a scientific name, but they belong to the genus Propostira. The researchers call them ballista spiders—after a Roman, crossbow-like weapon that could launch large rocks hundreds of metres.

The sequence of the hunt is precise. The spiders hide during the day on the underside of leaves. Shortly after dusk, they begin building the trap, a process that can take up to four hours to complete. During that time, the spider lays between 15 and 60 tightly bunched tension lines attached to a leaf, forming a conical shape.

Once the trap is built, the spider appears to rely on chemical cues as well as mechanical force. It applies a kind of chemical that triggers green tree ants—but not other species—to attack the trap with their mandibles. Narendra suspects the silk is sticky. “The mandibles are not able to actually able to open up and let it go and release; they are glued stuck.”.

When the ant strains against the snare, it tries to pull itself free and, in the process, releases the trap’s anchor point. At that exact moment, the tension lines fling the ant nearly 30 centimetres into the air. From there, the ant becomes tangled in the spider’s main web.

Why launch the prey like this?. Narendra argues it may be a way to lift the ant up and out of the colony’s direct attack path through the forest. helping the spider avoid a dangerous counterattack from the group. And he also frames the effort as something the spider can afford because its target is dependable.

Green tree ants, he says, are an extremely reliable food source. “Whenever the spider needs to eat, it just steps out, builds the web, and it’ll have food coming in.”

The story of the ballista spider is still being assembled—down to the fact that the animals studied so far remain unnamed in scientific terms. But the physics of their hunt is already clear: a conical trap. built at night. tuned to one ant species. and firing with accelerations that turn a meal into a sudden. airborne event.

ballista spider Propostira green tree ant Oecophylla smaragdina spider trap web snare ant predation biomechanics animal behavior Australia