Spiders use webs to hear, new study shows
Everyone knows that humans and most other species of vertebrates hear with the help of eardrums that convert sound wave pressure into signals for our brains. But what about small animals like insects and arthropods? Can they detect sounds? And if yes, how ?
Distinguished Professor Ron Miles, a faculty member in the Department of Mechanical Engineering at Binghamton University’s Thomas J. Watson College of Engineering and Applied Science, has been exploring this question for more than three decades, with the goal of revolutionizing technology. microphones.
A recently published study of orb-weaving spiders – the species featured in the classic children’s book “Charlotte’s Web” – yielded extraordinary results: spiders use their webs as extended auditory networks to pick up sounds, possibly giving be to spiders an advanced warning of the arrival of prey or predators.
The article, “Externalized hearing in an orb-weaving spider that uses its web as a hearing sensor,” published March 29 in the Proceedings of the National Academy of Sciencesprovides the first evidence that a spider can outsource hearing to its web.
It is well known that spiders react when something vibrates their webs, like potential prey. In these new experiments, the researchers show for the first time that spiders flip, crouch, or flatten in response to sounds in the air.
The study is the latest collaboration between Miles and Ron Hoy, biology professor at Cornelland this has implications for the design of highly sensitive bio-inspired microphones for use in hearing aids and cell phones.
Jian Zhouwho earned his Ph.D. in Miles’ lab and is doing postdoctoral research at Argonne National Laboratory, and Junpeng Lai, currently a PhD student in Miles’ lab, are co-first authors. Miles, Hoy and Associate Professor Carol I. Miles of the Department of Biological Sciences at Harpur College of Arts and Sciences in Binghamton are also the authors of this study. National Institutes of Health grants to Ron Miles funded the research.
A single strand of spider silk is so fine and sensitive that it can detect the movement of vibrating air particles that make up a sound wave, which is different from how eardrums work. Ron Miles’ previous research led to the invention of new microphone designs based on insect hearing.
“The spider is really a natural demonstration that this is a viable way to detect sound using viscous forces in the air on thin fibers,” he said. “If it works in nature, maybe we should take a closer look.”
Spiders can detect tiny movements and vibrations through sensory organs in their tarsal claws at the end of their legs, which they use to grasp their webs. Orb-weaver spiders are known to make large webs, creating a kind of acoustic antennae with a sound-sensitive surface that is up to 10,000 times greater than that of the spider itself.
In the study, the researchers used Binghamton University’s anechoic chamber, a completely soundproof room under the innovative technologies complex. Collecting orb weavers from campus windows, they instructed the spiders to weave a web inside a rectangular frame so they could position it wherever they wanted.
The team started by using pure sound from 3 meters away at different sound levels to see if the spiders were responding or not. Amazingly, they found that spiders can react to sound levels as low as 68 decibels. For a louder sound, they found even more behavior types.
They then placed the sound source at a 45 degree angle, to see if the spiders behaved differently. They found that the spiders not only located the source of sound, but could indicate the direction of incoming sound with 100% accuracy.
To better understand how spiders hear, the researchers used laser vibrometry and measured more than a thousand locations on a natural spider’s web, with the spider sitting centrally below the sound field. The result showed that the band moves with the sound almost with maximum physical efficiency over an ultra-wide frequency range.
“Of course, the real question is, if the web moves like that, does the spider intend to use it?” Miles said. “That’s a difficult question to answer.”
Lai added, “There might even be a hidden ear in the spider’s body that we don’t know about.”
The team therefore placed a mini-speaker 5 centimeters from the center of the web where the spider is located and 2 millimeters from the plane of the web, close to but not touching the web. This allows sound to travel to the spider both through the air and through the web. The researchers found that the sound wave from the mini-speaker died out significantly as it traveled through the air, but traveled easily through the web with little attenuation. The sound level was still around 68 decibels when it hit the spider. Behavioral data showed that four out of 12 spiders responded to this web-borne signal.
These reactions proved that spiders could hear through webs, and Lai was thrilled when it happened: “I’ve been working on this research for five years. It’s long, and it’s great to see that all of this effort will become something that everyone can read.
The researchers also found that by squatting and stretching, the spiders could change the tension of the strands of silk, thereby tuning them to pick up different frequencies. By using this external structure to hear, the spider might be able to customize it to hear different kinds of sounds.
Future experiments could investigate how spiders use sound that they can detect using their web. Additionally, the team would like to test whether other types of web spiders also use their silk to contract their hearing.
“It’s reasonable to guess that a similar spider on a similar web would react similarly,” said Ron Miles. “But we can’t draw any conclusions about that, since we tested a certain type of spider that happens to be quite common.”
Lai admitted he had no idea he would be working with spiders when he came to Binghamton as a graduate student in mechanical engineering.
“I’ve been scared of spiders all my life, because of their alien looks and hairy legs!” he said laughing. “But the more I worked with spiders, the more amazing I found them. I’m really starting to appreciate them.