The Surprising Discovery
Scientists have known for quite some time that spiders have exceptional vision, particularly jumping spiders. They’ve even known that spiders are able to feel nearby vibrations. But, because they don’t have ears, scientists believed they couldn’t hear at all. “The standard textbooks say that spiders are acutely sensitive to airborne vibrations from nearby sources, sounds about a body length or a few centimeters away. We have discovered that jumping spiders can hear things from much farther away than this,” says Gil Menda, co-researcher of Cornell University. This discovery actually happened by accident. The researchers were studying how spiders process visual information by making neural recordings of their brain activity. After taking a recording, Gil Menda moved his chair and it squeaked. “The way we do neural recordings,” explains Paul Shamble, co-researcher, “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.” Gil moved his chair again and the neuron popped again. Not convinced of what they were seeing, the two researchers started clapping. When the spider neurons responded, the researchers started moving farther away. They reached 5 meters away from the spider and the reaction continued. The two were amazed. “You thought they were just these little creatures of vibration and vision,” says Paul Shamble, “and now all of a sudden you realize that they can hear, too.”
The Research
Now that they knew spiders could hear, the team conducted additional research to figure out how. They tested spiders’ hearing by using both behavioral experiments and neural recordings. The behavioral experiments were done to determine the spiders’ reactions to sounds. The neural recordings were to determine which frequencies caused the spiders to respond. According to the experiment, spiders are most sensitive to low-frequency sounds of between 80 and 130 hertz (Hz). This frequency is the same as that emitted by the wingbeats of parasitoid wasps, a predator of spiders. Spiders freeze when they hear this sound, an anti-predatory behavior.
How Spiders Hear
If spiders don’t have ears, how is all of this even possible? Turns out, the hairs on their legs are sensitive to sound. Previously, scientists believed these hairs were only able to detect airborne vibrations from just a few centimeters away. This new discovery has shown that spiders process the vibration into neural activity. In other words, spiders are not simply sensing vibrations, but rather hearing. To test this, the researchers placed water on the spider’s legs in order to muffle the vibrations. The spider stopped firing auditory neurons, meaning the spider could no longer hear.
Significance of the Finding
This research only involved jumping spiders, but follow-up studies show that they are not the only ones with this ability. Fishing spiders, wolf spiders, net-casting spiders, and house spiders are all able to hear. And since most spiders have hairy legs, it is likely that others can hear too. Why does all of this matter? This finding could result in new technologies for people. In the future, devices such as hearing aids or microphones may include hairlike additions, resulting in improved performance. As Menda says, “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!” Which is exactly what we need, spiders with actual spidey-senses. Don’t let any of this worry you, though. If spiders are eavesdropping on our conversations, they can’t repeat anything they hear. It’s not like they have the ability to talk… or do they?
