Australia's Ballista Spider Flings Ants at 130 G With 30-Centimeter Snare Trap

Q: What secret chemical allows this spider to lure its most dangerous prey?

The spider appears to use a prey-specific pheromone, but researchers have not publicly identified the exact compound. According to the study, the ballista spider applies a chemical attractant to its conical silk trap that is tailored to green tree ants, *Oecophylla smaragdina*. Evidence suggests the substance provokes worker ants into an aggressive bite, which is exactly what triggers the snare. What is known, based on the reporting and supporting material, is that the lure is likely a pheromone or pheromone-like chemical mimic placed on the silk during the final stage of trap construction. That makes the trap chemically specialized for one dangerous prey species. What is not yet known from the published accounts is the “secret” formula itself: the researchers described its effect, but not the precise chemical identity. So the short answer is that the spider likely uses an ant-targeting pheromone mimic, but the exact chemical has not been disclosed.

Q: Why did this spider evolve a four-hour trap for only one dangerous ant species?

It likely evolved because green tree ants are both worth the effort and too dangerous to catch any simpler way. The evidence from the new study points to a highly specialized trade-off. Green tree ants are abundant, predictable and travel in regular trails, giving the spider a dependable food source. But they are also aggressive, strongly defended and able to recruit nestmates quickly. For a small spider, attacking one directly could trigger a swarm response. The four-hour trap appears to solve that problem. The spider builds a cone of 15 to 60 tension lines, adds a chemical lure that specifically provokes green tree ants, and lets the ant trigger the mechanism itself. When the ant bites and struggles, the stored elastic energy in the silk launches it about 30 centimeters into the air and into the main web. That removes the prey from the colony’s path almost instantly, reducing the risk of counterattack. Researchers say this is why such an elaborate design can still make evolutionary sense despite its cost. The spider is not trying to catch many kinds of prey; it is exploiting one dangerous but reliable species with a method tuned to that ant’s behavior, strength and aggression. In effect, the spider has evolved a safe way to harvest a rich food source that most predators would avoid. So the trap is expensive, but it buys two things evolution rewards: reliable meals and survival.

1 articles · Updated · New Scientist · Jun 22

Researchers in Australia found a newly discovered “ballista spider” that catches green tree ants by catapulting them nearly 30 centimeters into a larger web at up to 1,367 meters per second squared.
High-speed filming at 5,000 to 7,000 frames per second showed the spider builds a conical trap with 15 to 60 tension lines, then lures only green tree ants to bite it.
The ants appear to get their mandibles stuck on the silk, and their struggle releases the anchor point, letting the loaded snare spring and launch the prey upward.
Ajay Narendra's team says the tactic likely lifts prey off the ants' trail to avoid a colony counterattack, making the labor-intensive trap worthwhile because green tree ants are a reliable food source.
The nocturnal spider, observed in far north Queensland and not yet formally named, belongs to the genus Propostira, according to the Current Biology study.