Scientists have identified a previously unknown spider species in Australia that deploys an unusually specialized hunting strategy, using a spring-loaded silk structure to catapult only green tree ants into the air before capturing them in its web.
The unnamed species, believed to belong to the small genus Propostira, expands a group that previously contained just two known species. While it has not yet been formally classified, researchers say its behavior has already set it apart in striking ways.
What makes the spider remarkable is not only its hunting technique but its extreme dietary specificity. It feeds exclusively on green tree ants (Oecophylla smaragdina), ignoring all other ant species entirely — a level of selectivity rarely observed in arachnids.
“It is very unusual for a spider to prey on ants, because ants are dangerous,” said Prof. Ajay Narendra, the study’s lead researcher. “And it is even more unusual to find a spider that feeds on only one specific ant species.”
Green tree ants are known for their formidable defenses, including chemical signaling, strong mandibles and the ability to rapidly mobilize large numbers of nestmates in coordinated attacks.
During the day, the spider rests on the underside of leaves directly above ant foraging routes. At night, it begins constructing its trap, descending on silk threads to place anchor points roughly 50 centimeters below before assembling a conical structure composed of 15 to 60 silk lines.
Researchers describe the structure as a biologically engineered “masterpiece,” held under tension and storing elastic energy like a loaded spring. When disturbed, that energy is released almost instantaneously.
When ants encounter the structure, they typically respond aggressively, biting the silk cone. That reaction is precisely what triggers the trap. The anchor points detach, releasing stored tension and launching the ants upward at extreme acceleration before they land in the spider’s web above.
Narendra said the spider may also use chemical cues to provoke aggression. “It appears the final stage of construction involves a pheromone that specifically attracts and triggers attack behavior in O. smaragdina,” he said, suggesting the ants effectively activate their own capture system.
The mechanism is powerful enough to overcome the ants’ specialized adhesive footpads, which normally allow them to cling to nearly any surface and support forces exceeding 100 times their body weight.
“The ballista-like trap is biologically engineered to store elastic energy in silk and release it extremely quickly, delivering extraordinary instantaneous power density,” Narendra said, adding that it outperforms other known silk-based capture systems.
To test its specificity, researchers introduced three other ant species near the web. None interacted with or attacked the structure, reinforcing the conclusion that the trap is tailored exclusively to green tree ants.
Scientists say the findings suggest a highly evolved, species-specific predatory system unlike anything previously documented, in which both prey behavior and biochemical cues are integrated into the mechanics of capture.
The study has been published in the journal Current Biology.
