Spiders Lack Ears, But They Can Hear Through Their Leg Hairs

October 13, 2016 | Erica Tennenhouse

Photo credit: Thomas Shahan/Wikimedia (CC BY 2.0)

Study finds jumping spiders can detect sound at greater distances than previously thought.

Jumping spiders have no ears, but they can still hear you — even from a considerable distance.

Scientists noticed that when they played low-frequency sounds, jumping spiders would respond by freezing, which is “a common anti-predatory behavior characteristic of an acoustic startle response,” they write in the journal Current Biology.

RELATED: Jumping Spiders: Smarter than the Average Spider

The researchers were uncertain of whether the spiders were actually receiving the sounds directly via the air, or simply responding to vibrations that they could feel through other objects, like webs or leaves.

To find out, they placed the spiders — equipped with microelectrode brain implants — in boxes specially designed to block vibrations from below. When those same low-frequency sounds were played, the spiders froze in their tracks again. Their brain activity also spiked, not only in response to close-range sounds, but also to sound sources located more than 3 meters (10 feet) away.

“We were very surprised,” one of the authors of the study, Gil Menda of Cornell University, tells New Scientist. “Our studies extended the range of auditory sensitivity to more than 3 metres – over 350 body lengths – for our spiders.”

The spiders’ responses were much stronger when the sound frequency resembled that generated by the wing beats of their flying predators, especially wasps.

How do jumping spiders manage to detect these airborne sounds without the aid of ears or eardrums?

Direct stimulation of tiny hairs on the spiders’ legs generated a strikingly similar neural response to that produced when the spiders processed sounds, suggesting that these sensitive hairs are involved in sound detection.

“All spiders have these hairs, so it seems likely this is something that lots of spiders can do, as opposed to something exclusive to jumping spiders,” says first author Paul Shamble, from Harvard University. “This result really offers a new perspective on the auditory world of spiders, since we now know they can hear at much greater distances.”

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