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The next time you shriek at the sight of a spider, be aware that the arachnid can hear you loud and clear from as far as away as 10-feet! The surprising discovery by Cornell University researchers adds to the already impressive list of arachnid attributes that includes superior vision and ability to weave intricate webs.
Right about now, you are probably wondering how this is even possible given that spiders do not have ears. It turns out they do not need them. The arachnids use the minuscule hair on their legs to perceive vibrations through the air, or via the ground and walls, and convert them into neural activity. While this has been known for some time, scientists had always believed that the hearing capability extended to vibrations just a few centimeters, or a “spider’s length” away.
Gil Menda, the co-author of the study published in Current Biology on October 13, says the team stumbled upon the spider’s hearing prowess accidentally. The researchers were studying the Phidippus audax, a type of jumping spider they thought relied completely on sight and vibrations felt through objects like leaves or floorboards. However, when Menda’s chair squeaked, the metal microelectrodes implanted in the spider’s poppy-seed-sized brain registered the firing of its neurons, indicating that the arachnid had “heard” the sound.
To test if that was the case, Menda and his colleague Paul Shamble, now at Harvard, clapped right next to the spider, and then further and further out. Sure enough, its neurons kept firing until they were about 10-feet away! To confirm the spider was responding to the claps and not other air vibrations, the researchers conducted the experiment in an echo-free chamber and obtained similar results. “We were very surprised,” says Menda, “Our studies extended the range of auditory sensitivity to more than 3 meters – over 350 body lengths – for our spiders.”
The team then explored whether the leg hairs were indeed related to hearing by putting a water droplet on the spider’s legs. Sure enough, the moisture blocked the tiny hairs from sensing the vibrations, causing the spider to temporarily lose its “hearing” ability.
Menda and his team also discovered that the spiders “froze” when exposed to low-frequency sounds that resembled a hum or buzz (80 to 130 hertz). Further investigation revealed that this is the wingbeat frequency of their biggest predators — parasitoid wasps and flies. This means that spiders did not evolve this acute sense of hearing to eavesdrop on humans. They were just trying to stay alive!
While the research was conducted on jumping spiders, the team has since found that other spider species have the same “hearing” capabilities. Whether you think this is creepy or cool, one thing is for sure: there’s a lot more to the eight-legged creatures than spinning webs and featuring in Halloween decorations.
Resources: Newscientist.com, mirror.co.uk, npr.org