Gone are the days when you can gossip freely about your friends in the arachnid world. They don't have ears and were thought to mostly interpret the world around them through sight and touch, but scientists have now discovered that spiders possess the ability to hear over relatively long distances, a sense that appears finely tuned to recognizing the sounds of incoming enemies.
While spiders don't "hear" per se, it has long been established that they can sense vibrations through the hairs in their body just a few centimeters away, when changes in airflow cause these hairs to bristle. But now some clever science and a chance encounter with a squeaky chair has revealed the true extent of the creature's listening capabilities.
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Scientists at Cornell University were conducting an experiment designed to study the neural activity of the jumping spider. They did this by slipping an electrode the size of a hair through a tiny hole in the head, which then closes around the wire like a self-sealing tire. These microelectrodes then record electrical spikes as neurons fire in response to stimuli.
Gil Menda, a postdoctoral researcher at Cornell, was actually using this technique to examine the animal's visual perception, but got a surprise when neurons suddenly fired after his chair squeaked. He and his team soon worked out that the spider could sense far-field sounds over distances as great as three meters (9.8 ft), or about 600 spider body lengths. He proceeded to explore how the brain reacted to a range of audio frequencies, and then began to wonder why the spiders seemed especially sensitive to some frequencies and not others.
As it turns out, a frequency of 90 Hz is close to that of a parasitic wasp's flapping wings, who just happens to be the jumping spider's biggest predator. In a follow-up experiment, the scientists played sounds at 90 Hz and found that 80 percent of the spiders in the study froze up for a second, before turning and jumping. This behavior was seemingly meant to allow the spider to go unnoticed while the wasp scans the area for movement, before quickly turning and making a run for safety.
Since the discovery, the team has found evidence of the same phenomenon in five other spider species: jumping spiders, fishing spiders, wolf spiders, netcasting spiders and house spiders. It will now focus on further investigation of audio neurons in the spider's brain, something it says could one day lead to hair-like structures for extremely sensitive hearing aids.
The research was published in the journal Current Biology, and you can hear from the researchers in the video below.
Source: Cornell University