Jumping Spiders Can Hear Sound Despite Having No Ears
Spiders have no ears or eardrums, and conventional wisdom has held that they are only able to sense airborne vibrations from a few centimeters away. Now, researchers have found that jumping spiders — and most likely other spiders as well — can actually hear sounds over much greater distances.
“The sensory world of the tiny jumping spider was thought to be dominated by sight and tactile touch,” said Paul Shamble, who conducted the work along with colleagues in Ron Hoy’s lab at Cornell University. “Surprisingly, we found that they also possess an acute sense of hearing. They can hear sounds at distances much farther away than previously thought, even though they lack ears with the eardrums typical of most animals with long-distance hearing.”
Their discovery was a lucky accident. Shamble and colleagues, including Cornell University’s Gil Menda, had previously devised a new method for making neural recordings from the brains of jumping spiders, and they were using the technique to explore how jumping spiders process visual information. But one day noise from a squeaky chair caused a rection in the spider’s brain.
“One day, Gil was setting up one of these experiments and started recording from an area deeper in the brain than we usually focused on,” Shamble said. “As he moved away from the spider, his chair squeaked across the floor of the lab. The way we do neural recordings, 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. He did it again, and the neuron fired again.”
“We started discussing the details about how spiders can only hear things close by,” Menda continued, “and to demonstrate, Paul clapped his hands close to the spider and the neuron fired, as expected. He then backed up a bit and clapped again, and again the neuron fired.”
Soon, Menda and Shamble were standing outside the recording room, three to five meters from the spider, amazed as the spider’s neuron continued to respond to their clapping. Based on everything they thought they knew, it shouldn’t have been possible.
Further study showed that the jumping spiders’ hearing is most sensitive to frequencies that would enable them to hear the wingbeats of their parasitoid wasp enemies. Behavioral experiments have shown that jumping spiders respond to such sounds by freezing — a common startle response.
So how do spiders hear if they have no ears? The researchers believe that they probably feel vibrations from tiny hairs on their legs called trichobothria. They found that direct mechanical stimulation of the hairs was enough to generate a response in acoustically sensitive neurons.
“When we shook single sensory hairs back and forth — these are the same hairs that are known to respond to sounds originating close to the animal — we also got responses,” Shamble said. “This suggests that these hairs are how spiders are registering far-away sounds.”
“In the movies, Spiderman has this strange, additional ‘spidey sense’ that helps him sense danger,” Menda said. “It turns out the real-life spidey sense of spiders might actually be hearing!”
The researchers are now recording from the brains of fishing spiders, wolf spiders, and others to test their hearing too.
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