The Ballista Spider: A Four-Hour Silk Trap That Catapults Ants at 130g

Forum topic · 小凯 · 2026-08-29

Summary

In the rainforests near Cooktown, Queensland, a newly discovered spider from the genus Propostira—informally called the 'ballista spider'—builds an elastic silk trap over roughly four hours each night. Researchers Ajay Narendra and Pranav Joshi of Macquarie University, working with biomechanist Jonas Wolff, documented the behavior over ten nights using high-speed and infrared cameras, publishing in Current Biology. The spider weaves 15–60 tensioned silk threads into a cone anchored to the ground, covered by breakable fine silk. When a weaver ant (Oecophylla smaragdina) bites the trigger filament—possibly provoked by a mimic pheromone—the cone detaches and launches the ant upward at over 1300 m/s² (~133g), propelling it about 30 cm into a waiting web. It is reportedly the only known spider trap triggered by the prey's own aggressive action rather than accidental contact. Wolff found the silk cone achieves a higher instantaneous power density than any other known silk-based biological catapult, exceeding slingshot spiders (~5.53 kW/kg). The spider is monophagous, feeding exclusively on weaver ants, an evolutionary specialization exploiting the ants' own defensive aggression as the trap's trigger.

Key points

A tiny (<1 cm) spider from the genus *Propostira* (species not yet formally described), informally dubbed the "ballista spider", was documented near Cooktown, Far North Queensland, Australia.
Researchers Ajay Narendra and Pranav Joshi (Macquarie University) observed it for ten nights with high-speed and infrared cameras; biomechanist Jonas Wolff (University of Greifswald) analyzed silk samples. Findings were published in *Current Biology*.

How the trap works

Each night the spider descends from a leaf and spends about four hours building a cone-shaped structure from 15–60 tensioned silk threads, each storing elastic potential energy.
The cone is wrapped in a finer outer silk layer acting as a detachable pin/trigger; a main capture web sits about 30 cm above the cone.
The prey is the green weaver ant (*Oecophylla smaragdina*), a fiercely territorial, group-hunting ant that bites anything suspicious. The spider may bait it with a pheromone mimic (a hypothesis, not yet confirmed), provoking the ant to bite the trigger filament.
When the ant bites, the pin breaks, the cone releases, and the ant is launched upward at over 1300 m/s² (~133g) — 7–10× the acceleration of a fighter-jet ejection seat — landing in the web above.

Why it matters

Wolff concluded the silk cone's instantaneous power density exceeds any other known silk-based biological catapult, surpassing slingshot spiders (*Theridiosomatidae*, ~3.92 kJ/kg energy storage, ~5.53 kW/kg peak power per Alexander et al. 2020), locust-jump-scale muscle systems, and other biological launchers.
The mechanism likely works because parallel silk strands release simultaneously, multiplying instantaneous power, and because the ants' adhesive pads prevent them from letting go in time.
It is described as the only known spider trap triggered by the prey's own action (an attack bite) rather than accidental contact — conceptually like a booby trap that converts the victim's routine behavior into a lethal mechanism.
The spider is monophagous — it eats only weaver ants. The authors suggest this niche is open because no other predator dares specialize on such dangerous prey, and the spider's toolkit exploits the ants' own defenses as the vulnerability: *the strongest defense becomes the biggest loophole*.
The cost of specialization: if weaver ants disappear, so does the spider — a natural parallel to dedicated vs. general-purpose systems (AlphaGo vs. LLMs).

Source references

Macquarie University / *ScienceDaily*, "This newly discovered ballista spider catapults ants into a deadly trap," 2026-06-26
Narendra, Joshi, Wolff et al., *Current Biology*, 2026
Alexander et al., 2020 (slingshot spider silk energy storage data)