Date:20 October 2016
A new study has discovered that jumping spiders have a far acuter sense of hearing than previously thought.
Traditionally, the sensory world of jumping spiders was thought to be dominated by sight and touch. Not so, according to a study released today in Current Biology. Neural recordings of jumping spiders’ brains show that they are able to respond to sounds over distances of more than three meters.
The findings add an entirely new auditory dimension to our understanding of spiders, which unlike most animals with long distance hearing, lack ears with eardrums.
“The standard textbooks say that spiders are acutely sensitive to airborne vibrations from nearby sources, sounds about a body length or a few cm away,” says Gil Menda, Cornell University. “We have discovered that jumping spiders can hear things from much farther away than this. Interestingly, it seems that in both cases, this “hearing” is accomplished by sensory hairs.”
Jumping spiders’ hearing is tuned to low frequency tones that would alert them to the wingbeats of flying predator insects such as parasitoid wasps and predatory flies, says Menda. These hairs are something that most spiders possess, so Menda and his colleague Paul Shamble of Cornell University believe that this is something all spiders should be able to do, not just jumping spiders.
The discovery also happens to be a lucky accident. At the time, Menda and Shamble were making neural recordings of jumping spiders’ brains to explore how they process visual information using a method from a previous paper.
“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,” says Shamble. “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.”
The two began talking about what was previously known about the hearing of spiders, specifically that they are only meant to hear things close-by.
“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, we were standing outside the recording room, about 3-5 meters from the spider, laughing together, as the neuron continued to respond to our clapping. Based on everything they knew it shouldn’t have been possible, but there it was. It was just the beginning of months and years of work, but it was an incredible start,” says Menda.
Sound wasn’t the only thing that generated a response in the spider’s acoustically sensitive neurons. By shaking single sensory hairs on the spiders back and forth Menda and Shamble got the same responses, suggesting that these hairs are how the spiders are registering sounds from greater distances.
The addition of hearing to the sensory world of the jumping spider makes these creatures all the more amazing, particularly because they can do all of this with such small brains. Understanding how this is possible will fall within the field of spider neuroethology, which according to Mena has just opened for business.
The spider man movies will also have to catch up.
“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!” says Menda.
The video above explains the recording process and gives in-depth insight into the research.