Armed with a weighted net, a three-pointed trident and a dagger, the retiarius – or fisherman gladiator – was a familiar sight in Rome’s ancient arenas. Their survival depended on swiftly ensnaring heavily armoured opponents with the specially designed nets.
Surprisingly, certain spiders employ a strikingly similar technique. Slingshot spiders (Theridiosoma gemmosum), also known as ray spiders, create a unique trap by pulling the centre of their flat web into a cone, holding it taut with a single anchor thread.
When prey approaches, they release the thread, propelling the web forward like a catapult to entangle their target in its sticky threads.
In 2021, researchers Saad Bahmla (Georgia Institute of Technology, USA) and Todd Blackledge (University of Akron, USA) discovered that these spiders could be prompted to deploy their ballistic webs simply by the sound of a finger snap. Could these arachnids actually be listening for their prey, releasing their nets even before the unsuspecting victims touch the web?
To investigate, Blackledge and his colleague Sarah Han conducted experiments to test the spiders’ sensitivity to sound. Their findings, published in the Journal of Experimental Biology, revealed that slingshot spiders indeed appear to ‘hear’ their prey, timing their web launches to intercept insects as they come within range.
“Slingshot spiders are really tiny, so they can be quite hard to find,” explains Han, recalling hours spent looking for their distinctive cone-shaped webs along riverbanks at several locations in the Summit Metro Parks of Ohio, USA. “It does take some time to develop the eye for them,” she admits.
Once Han had collected the spiders, she recreated their natural environment in the lab, providing twigs for web-building and hunting down mosquitoes to serve as bait.
The results were fascinating. When a mosquito came close, the spiders released their webs to capture it – but the insects didn’t actually need to make contact with the web.
The spiders could launch their nets before any physical impact occurred. Intrigued, Han used a tuning fork tuned to mimic the sound of mosquito wings and found the spiders responded just the same, hurling their webs forward at the phantom insect. This indicated that the spiders were detecting sound, likely with the sensitive hairs on their legs, to identify the presence of prey.
The speed of these attacks is astounding, says Han, who calculated that the spiders’ webs accelerate at a staggering 50g (504m/s²), reaching velocities close to 1m/s and intercepting their target in just 38 milliseconds – far too fast for the prey to escape.
Moreover, the spiders displayed remarkable precision: they were much more likely to release their webs when a mosquito was directly in front (76%) compared to when it was behind the web (29%).
Han and Blackledge suggest the spiders may compare vibrations transmitted through their web with those carried through the air to determine the insect’s position, ensuring their strikes hit the mark.
These remarkable little hunters demonstrate a level of ingenuity and precision worthy of their gladiator-like reputation, proving that even the tiniest predators have evolved some of the most extraordinary strategies in the natural world.
Find out more about the study: Directional web strikes are performed by ray spiders in response to airborne prey vibrations
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