Imma Perfetto
Cosmos science journalist
Unlike spiders that wait for unsuspecting prey to blunder into their webs, the slingshot or ray spider (Theridiosoma gemmosum) is a more proactive hunter.
Lying in wait, it attaches a tension line to a nearby twig or rock and pulls back the centre of its web into a cone. On releasing this tension line, the web snaps back like a slingshot to intercept and capture an insect mid-flight.
But how does the spider know when its prey is in range? Researchers in the US have discovered slingshot spiders sense the vibrations of an airborne insect’s flapping wings.
They attached individual mosquitos to strips of black paper but left their wings free to flap as if flying and waved the insects close to the spider’s web while filming the interaction.
The videos revealed the insects never touched the webs with their protruding front legs before the spider released its web cone. They were also more likely (76%) to release the web when the mosquito was in front of it, rather than when it was behind (29%).
Waving a tuning fork, pitched at the same tone produced by the mosquitoes’ wings, confirmed the spiders must be “hearing” the airborne vibrations of the insects’ approach.
The researchers suspect that the spiders may determine prey’s direction of approach by comparing how they perceive sound transmitted through the web to their bodies with sound vibrations carried through the air to the sensitive hairs on their legs.
“These data support our hypothesis that ray spiders can detect flying prey solely through airborne vibrations,” the researchers write in their new paper in the Journal of Experimental Biology.
“And that one of the functions of the ray spider’s web release may be to attack flying insects that would otherwise sense and avoid a static orb web.”
