Clever hunter: the web spider in this photo has just spun a safety net that it holds in place with its front legs. If she discovers an insect, she throws the net over her victim in a flash – and even flips backwards.
Throwing web spiders (Deinopis) owe their name to their nocturnal hunting technique: They spin – hanging on a thread above the ground – a safety net that they hold between their front legs. With their large central eyes, the spiders can recognize insects on the ground even in the dark and then put their web over the victim in seconds. While this hunting method sounds unusual, the spider web spider, native to the southeast of the USA, has an even more curious trapping strategy: It preyes on flying insects behind it that it cannot see and does an acrobatic backward flip.
But how does the eight-legged friend notice the flying insects? For a long time it was believed that spiders only perceive air vibrations and sound from their immediate surroundings with their sensory hair, because they have no real hearing organs. However, the hunting method used by the web spiders suggests that the animals must have heard their prey before jumping.
This is exactly what a team of researchers led by Jay Stafstrom from Cornell University has now investigated: In their experiment, the scientists found that the web spiders have much better hearing than previously thought. According to this, these spiders not only recognize vibrations close by with their sensory hairs, but also hear sounds from over two meters away with the help of receptors on their front legs. In addition, the spiders from the experiment reacted reflexively to low sounds, similar to the hum of a flying insect, with their acrobatic backflip – the sense of hearing seems to enable their unusual trapping strategy.
Next, the researchers now want to test whether the web spiders can also recognize where noises are coming from. “Directional hearing is a big deal with any animal, but I think there will really be some interesting surprises from this spider,” says Stafstrom’s colleague Ron Hoy. Because if the web spiders also hear directionally, this could further explain their acrobatic hunting style, according to the scientists.