A new spider species found in the tropical rainforests of Australia has amazed scientists with its unique hunting method that propels prey through the air using a silk trap loaded with springs. The discovery, detailed in a recent publication in the journal Current Biology, showcases how this small arachnid constructs a cone-shaped snare to launch green tree ants into its web, earning it the moniker “ballista spider,” reminiscent of the ancient Roman weapon used for hurling heavy objects.
Ajay Narendra, a biology professor at Macquarie University in Australia and one of the study’s main investigators, expressed awe at witnessing the spider’s behavior. Belonging to the Propostira genus, this spider is yet to be formally named as a new species.
The first sighting of this spider occurred in 2022 when researcher Greg Anderson observed a green tree ant being flung into a web in a remote rainforest on Queensland’s Cape York Peninsula. This event led a team from Macquarie University to investigate further in 2023. Using high-speed cameras, the researchers spent 10 days observing the spider’s unconventional hunting tactics. The initial attack they witnessed was so rapid that they missed recording it but were able to document subsequent instances due to the predictable nature of the spider’s behavior.
Measuring three to five millimeters in length, these nocturnal spiders hide under leaves during the day and emerge after sunset to construct intricate traps below their primary webs. By anchoring silk tension lines between 15 and 60 to a lower point, such as a leaf or branch, the spiders create a cone-shaped structure that, when triggered by green tree ants, releases stored tension, launching the insects up to 30 centimeters into the air. The launched ant lands in the spider’s main web, where it becomes the predator’s prey.
Green tree ants are swiftly attracted to the trap after the final silk layer is laid, suggesting the use of pheromones to specifically lure these ants. This specialized silk seems to exclusively attract green tree ants while being disregarded by other ant species found in the same vicinity.
Narendra speculates that this passive hunting approach is an evolutionary strategy to capture green tree ants, known for their collective strength, without direct confrontation. Further research is planned to analyze the spider silk and identify potential pheromones involved in this prey specialization.
The launch mechanism, occurring in a mere 42 milliseconds, subjects the ants to approximately 15 times the G-force experienced by jet pilots. This force exceeds that of the slingshot spider, a different species employing a similar hunting method. The ballista spider, unlike the slingshot spider, stores energy in its silk trap, enabling it to launch prey with significant force while maintaining a safe distance.
Saad Bhamla, an associate professor at the University of Colorado-Boulder’s BioFrontiers Institute, proposes a more straightforward explanation for the spider’s prey targeting, suggesting that the aggressive nature of green tree ants prompts an immediate response to any objects built in their vicinity.
The discovery of this remarkable hunting behavior showcases the ongoing discoveries in nature and the mysteries yet to be unraveled.