Ballista: A New Spider With a Catapult‑Like Silk Trap Captures Green Tree Ants

Researchers from Macquarie University have identified a previously unknown species of spider that has evolved a unique hunting technique in the rainforests of northern Queensland. The tiny arachnid, now informally dubbed the "ballista", constructs a special overflow trap that launches aggressive green tree ants (Oecophylla smaragdina) into its main silk web with breathtaking force.

Using high‑speed and infrared cameras, the team observed the spider’s nocturnal routine: after resting in hidden webs beneath the undersides of leaves during daylight, it descends to a leaf or branch, anchors itself with a silk line, and then painstakingly builds a cone‑shaped scaffold of dozens of tension lines. Once a green ant is entangled and bites the trigger, the tension lines recoil like a spring, flinging the insect into the spider’s larger capture web at roughly 15 times the g‑force experienced by commercial jet pilots.

"The mechanism seems to have evolved to allow the spider to isolate a dangerous prey item and relocate it safely away from ant trails and nests," explained lead researcher Prof Ajay Narendra. "The ant’s chemical defenses and ability to call for reinforcements make it a formidable target, so the spider’s design provides a high‑precision solution."

Remarkably, the ballista spider prefers this prey to other nocturnal ants in the same environment. The investigators speculate that the spider may incorporate pheromones into the trap to lure and agitate green tree ants specifically, although further study is required to confirm this hypothesis. This hunting adaptation marks the first known case where a spider’s web is engineered to target a single prey species and is activated by the prey’s own actions rather than by the spider’s sensory cues.

Published in the journal Current Biology, the study underscores the extraordinary diversity of arachnid hunting strategies and raises new questions about the evolutionary pressures that drive such specialized adaptations in tropical ecosystems.