Researchers have documented a novel hunting strategy in a nocturnal spider of the genus Propostira in the tropical rainforests of Cape York Peninsula, Queensland, Australia. The spider constructs a spring-loaded silk snare that is triggered by green tree ants (Oecophylla smaragdina). The findings were published in Current Biology by scientists from Macquarie University.
Discovery and Habitat
The spider, referred to as the ballista spider, was observed in the rainforests of northern Queensland. During the day, the spider rests under leaves. At night, it descends on a silk line to begin constructing its trap.
Mechanism of the Snare
The spider builds a fan-shaped web of silk tension lines by descending on a silk line to find an anchor point, then returning to its core web, leaving a tension line. This process is repeated to form a small conical scaffold, which is then wrapped with a thinner silk.
The thinner silk appears to attract green tree ants and provokes an attack response, possibly via pheromones. When an ant bites the cone, the cone detaches. This action propels the ant into the core web in a fraction of a second. The spider then wraps the entangled ant in silk for later consumption.
The snare releases with acceleration up to 1,367 meters per second squared (approximately 140 times gravity).
Performance
The snare's energy performance exceeds other silk-based catapult systems. According to the researchers, one kilogram of the web stores 78.17 kilojoules of kinetic energy and can briefly exert 11.73 megawatts of power. The trap stores more energy and exerts more power than any known biological catapult.
Prey Specialization
The ballista spider exhibits extreme specialization, preying almost exclusively on green tree ants. The snare is triggered by the prey itself, unlike typical predator-activated snares.
Background on Prey
Green tree ants are aggressive, territorial, and have chemical defenses including stings and the ability to recruit backup. Researcher Dr Jonas Wolff stated that the snare evolved to allow the spider to capture hazardous prey one at a time and transport them safely away from ant trails.
Significance
Lead researcher Prof Ajay Narendra stated the snare's mechanism flings ants at extreme acceleration. The findings demonstrate how extreme prey specialization can drive the evolution of exceptional biomechanical performance, according to the researchers.