A newfound spider species in the tropical rainforests of Australia has astonished scientists with its hunting method that propels prey through the air using a silk trap armed with a spring-loading mechanism.
The discovery, detailed in a study released by the journal Current Biology, showcases how this small arachnid constructs a cone-shaped snare to fling green tree ants into its web, earning it the moniker “ballista spider” in reference to the ancient Roman weapon used for launching heavy objects.
Ajay Narendra, a biology professor at Macquarie University in Australia and a key researcher in the study, expressed awe at witnessing the spider’s behavior firsthand, describing it as a breathtaking experience. The spider, identified as part of the Propostira genus, is yet to be formally classified.
The initial observation of this spider was made in 2022 by researcher Greg Anderson, who saw a green tree ant unexpectedly propelled through the air and ensnared in a web in a remote rainforest on Queensland’s Cape York Peninsula. Subsequently, a team from Macquarie University journeyed from Sydney to northern Queensland in 2023 to investigate further.
Utilizing high-speed cameras, the researchers spent ten days documenting the spiders’ unique hunting technique. The rapidity of the first attack witnessed by the team was so swift that they missed recording it entirely. However, they were able to capture subsequent instances as the spiders repeated their behavior consistently.
These spiders, measuring between three to five millimeters in length, are nocturnal creatures that remain hidden under leaves during the day. After sunset, they emerge and spend several hours crafting an intricate trap beneath their primary web. The trap is set by descending about half a meter and affixing between 15 to 60 silk tension lines to a lower anchoring point, such as a leaf or branch. These lines are then bundled into a tight cone structure and enveloped in finer silk.
Green tree ants are lured to bite the cone and become ensnared. As they struggle, the trap disengages from its anchor point, releasing the stored tension and launching the insect nearly 30 centimeters into the air. The ant lands directly in the spider’s main web, where it becomes prey.
The researchers observed that the green tree ants were attracted to the trap within a minute of the final silk layer being placed. This led them to speculate that the silk may emit pheromones specifically targeting these ants.
Narendra believes that this method reflects an evolutionary strategy to capture green tree ants, known for their formidable nature and group strength, without direct confrontation. Further analysis of the spider silk is planned to ascertain the possible use of pheromones for prey specialization.
Saad Bhamla, an associate professor at the University of Colorado-Boulder’s BioFrontiers Institute, suggests a simpler explanation for how the spiders select their prey. He proposes that the green tree ants’ aggressiveness and vigilance might prompt them to investigate any structures in their vicinity, such as those built by the spiders.
The launching mechanism of the ballista spider exerts significant force on the ants, subjecting them to approximately 15 times the G-force experienced by jet pilots in just 42 milliseconds. This force surpasses that generated by the slingshot spider, a different species employing a comparable hunting tactic.
Unlike the slingshot spider, the ballista spider does not face limitations on force due to the design of its silk trap, enabling it to launch prey with substantial force while maintaining a safe distance.
Overall, this discovery highlights the ongoing revelations in nature and the continuous potential for new findings in the natural world.
