Anewly identified spider from the tropical rainforests of northern Australia has unveiled a hunting technique unlike any previously recorded. The species, dubbed the “ballista spider,” uses a spring-loaded silk trap that launches green tree ants into its web at accelerations reaching 140 times the force of gravity, researchers report in Current Biology.
The discovery was made in the Cape York Peninsula in Queensland, where scientists observed the small nocturnal spider of the genus Propostira. While spiders are renowned for their diverse hunting methods, this species relies on a highly specialized trapping mechanism that appears tailored to a single prey species.
The finding expands the known range of spider hunting strategies. Net-casting spiders throw silk nets over prey, while slingshot spiders use tensioned webs to propel themselves toward a target. The ballista spider, by contrast, creates a trap that remains dormant until the prey activates it.
A Carefully Engineered Silk Snare
During daylight hours, this web-spinner remains hidden inside a silken retreat attached to the underside of leaves. Once night falls, it begins assembling a trap through a series of precise movements.
As described in Current Biology00570-1), the silk hunter descends on a silk line to establish anchor points before repeatedly returning to the center of the web. This process creates a fan-shaped arrangement of tension lines that gradually forms a small conical scaffold.
The cone is then wrapped in a thinner type of silk, producing a spring-loaded structure capable of storing significant amounts of energy. Researchers observed that the spider methodically repeats the same sequence until the trap is complete.
Unlike conventional webs designed to intercept prey passively, this mechanism relies on a specific interaction with the target species. The trap remains in place until an ant makes contact with it.
An Ambush Designed for Green Tree Ants
The ballista spider appears to focus exclusively on the green tree ant (Oecophylla smaragdina), an insect known for its aggressive behavior and strong colony defense.
The research team suggests that the silk covering the cone may contain pheromones or other chemical cues that attract ants and provoke an attack response. Shortly after the wrapping silk is added, worker ants often arrive and begin investigating the structure. Rather than avoiding the unfamiliar object, the ants attack it. The critical moment occurs when an ant bites the cone.
The Macquarie University reports that this bite detaches the cone from the surface, releasing the energy stored within the tensioned silk lines. The ant is then pulled upward and launched into the spider’s core web in a fraction of a second. Only after the prey is fully entangled does the spider approach. It then wraps the captured ant in silk before feeding.
Silk Catapult Sets Record
Measurements collected during the study revealed the extreme forces involved in the trapping process. Researchers recorded accelerations of up to 1,367 meters per second squared, equivalent to approximately 140 times the acceleration due to gravity.
The authors note that these forces are about 15 times greater than the most extreme g-forces experienced by jet pilots.
The performance of the trap also surpassed that of other known silk-powered biological catapults. Findings indicate that, gram for gram, the ballista spider’s web stores more energy and generates more power than any previously documented silk-based system.
Calculations showed that a kilogram of the web would store 78.17 kilojoules of kinetic energy and briefly produce 11.73 megawatts of power.
The researchers propose that this exceptional power enables the spider to pull ants away from nest areas and foraging trails before nearby colony members can respond. The study also highlights two unusual characteristics of the species: its apparent specialization on a single prey species and its reliance on prey-triggered capture.
