Spiders Can Hear You From Several Meters Away – Even Without Any Ears

Jumping spiders use more than just their eyes to see the world. Gil Menda and the Hoy lab

Spidey senses are tinglier than we could ever have imagined, according to a new study that reveals how the hairs on jumping spiders’ legs are able to detect vibrations in the air from several meters away, allowing the sensitive arachnids to pick up distant sounds.

Prior to this discovery, which is documented in the journal Current Biology, it had been assumed that jumping spiders lived in a predominantly visual universe, using their multiple eyes to register the world around them. Lacking anything that could pass for an eardrum, the creatures were considered more or less deaf to most noises, although their leg hairs – known as trichobothria – were thought to be able to detect nearby vibrations.

However, the idea of the silent spider sensory sphere has now been shattered by a group of researchers who stumbled upon the creature’s hearing abilities by accident. By implanting tiny electrodes into the brain of a jumping spider, the team had intended to observe how its brain reacted to certain visual cues.

In a statement, study co-author Paul Shamble revealed how his colleague Gil Menda unintentionally set off the spider’s neurons by making noise: “As he moved away from the spider, his chair squeaked across the floor of the lab. The way we do neural recordings, we set up a speaker so that you can hear when neurons fire – they make this really distinct 'pop' sound – and when Gil's chair squeaked, the neuron we were recording from started popping. He did it again, and the neuron fired again.”

The researchers then found that the same response occurred when the spider heard them clapping from more than 3 meters (10 feet) away. To confirm that these sounds were being picked up by the trichobothria, the researchers wiggled individual hairs on the spider’s legs and discovered that this did indeed produce the same brain response.

Because clapping produces white noise – meaning it contains a wide range of frequencies – the team then exposed the spider to a sequence of pure tones in order to figure out which of these it was most sensitive to. This test revealed that jumping spiders’ brains are fine-tuned to detect sounds with low frequencies, ranging from 80 to 130 Hertz.

Interestingly, this is the same frequency range as that produced by the wasps that prey on these spiders. When exposed to these tones, the spider froze in fear, indicating that it has evolved the ability to detect the audible signals given off by its main predators, even when a considerable distance away.

"In the movies, Spiderman has this strange, additional 'spidey sense' that helps him sense danger – it turns out the real-life spidey sense of spiders might actually be hearing," added Menda.

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