Researchers have identified a new hunting strategy in a tiny nocturnal spider found in tropical rainforests on Cape York Peninsula in Queensland, northeastern Australia. The animal, a Propostira spider that has not yet received a formal scientific name, has been nicknamed the “ballista spider” because it uses a spring-loaded silk trap to launch prey into its capture web. The study was published in Current Biology.
The team observed the spider for 10 nights using high-speed and infrared cameras. During the day, it rests inside a silk retreat under leaves above the foraging paths of green tree ants, Oecophylla smaragdina. At night, it descends about 50 centimeters or more on a silk line, anchors a cone-like structure to a leaf, branch, or the forest floor, and repeats the process to build a web of tension lines over several hours.
Once the trap is complete, the spider wraps the cone in a thin layer of silk and retreats. Within seconds, nearby green tree ants react aggressively, bite the structure, and detach its anchor point, which catapults the ant into the core web at acceleration of up to 1,367 meters per second squared, about 140 times gravity. Professor Ajay Narendra of Macquarie University, who led the study, said the spider may add a pheromone in the final stage to provoke the ants, and that this may be the only known case in which a spider web is designed for a single prey species and triggered by the prey itself.
After the ant becomes entangled in the lower web, the spider waits until it can safely approach, then wraps the prey in silk and feeds. The researchers think the trap evolved to quickly remove ants from their nest areas and travel routes, since the ants can summon hundreds or even thousands of nestmates in response to danger. Co-author Jonas Wolff, who studies the biomechanics of spider silk at the University of Greifswald in Germany, analyzed silk samples from the spider, including scanning electron microscopy, and said the mechanism lets the spider collect dangerous prey one at a time, away from ant colonies. Narendra added that the trap is “biologically engineered” to store elastic energy and release it faster than any other known silk-based biological ballista.
