Scientists have discovered a new kind of spidey sense.
We already knew that jumping spiders have exceptional vision. We knew that they are great at perceiving vibrations. We even knew that they can "hear" at extremely close range.
But in research published in Current Biology, researchers at Cornell University found that a common species of jumping spider called Phidippus audax can actually hear from much farther away than we thought — at distances of 10 feet away, or more.
"I've worked with these animals for a long time now and all of a sudden you realize that their world is completely different from what you thought," Paul Shamble, a fellow at Harvard and co-first author of the study, tells The Two-Way. "You thought they were just these little creatures of vibration and vision, and now all of a sudden you realize that they can hear, too."
Spiders don't have ears, as Shamble explains. He says humans pick up pressure waves to detect sound, while it appears that these spiders are able to "hear" because they have "specialized hairs that pick up the actual particle movement."
Take a look at this video released by the research team of a spider's response to a low-frequency sound:
The researchers actually discovered this by accident, he adds. It started with a fortuitous chair squeak.
"We were doing these studies on how the brains of jumping spiders perceive vision," he explains, using technology that actually allowed them to hear neurons firing in a spider's brain. Shamble's colleague and co-author Gil Menda was working in the lab when he backed up his chair, which let out a loud squeak.
"The neurons started firing and he thought, oh, that's kind of weird," Shamble says. To test this, Shamble clapped — first, right next to the spider. The neurons fired. He continued to back up, expecting the firing to stop, because they thought spiders could "hear" only at very close range.
"It kept on happening. And after a while I was standing out in the main lab, more than 3 meters away from the spider, clapping, and it was still happening," he says. "It was one of those strange moments, where it was like, based on what we know, this shouldn't be happening, but it definitely is."
Shamble says the researchers tested the spiders' hearing using both behavioral experiments (where they observed the spiders' reaction to sounds) and neural recordings (where they could determine "exactly what frequencies they were responding to").
The spiders tended to "freeze" in place when they heard a low-frequency sound, which Shamble says is likely an anti-predator response.
That's backed up by the neural recordings because the frequencies that spiders would respond to "are relatively low and they're right in the range of frequencies for especially sort of largish flying insects," Shamble says. That suggests the hearing could be a way to detect predators such as wasps.
There could be other uses for the "hearing" ability, too, he says, noting that jumping spiders have "really elaborate courtships."
They set up the experiment to make sure the spiders were responding to sound traveling through the air and not vibrations in the room.
Phiddipus audax and its close relatives are among the most common types of jumping spiders in the United States. Shamble says their research raises an important question — "is this something special to jumping spiders, these jumping spiders, or is this something that is sort of an underappreciated feature of all spiders?" He says he suspects other spiders can do this, too.
Knowing that spiders can detect sounds at long range changes the way we think about how they perceive the world.
"It's really exciting to realize that these creatures that have sort of lived next to us for as long as humans have been around, that there are these little mysteries that we didn't really know about how they live and how they make their lives," Shamble says.
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