In the story Charlotte’s net, the spider wrote messages on her web. Now it seems that some spiders are listening with that silk. One could now think of these nets as ears - replaceable ears.
Most animals have something like a tympanic membrane that responds to sound. Spiders don’t. They feel vibrations through their legs. This helps them know when their silkworm has caught a meal of insects. A new study reveals that spiders also use their webs to listen to sound. Moreover, they can customize the web to change the way they hear.
A thin network in the shape of spider bridge wheels acts as a super-sensitive antenna for capturing the sound movements of air particles, a new study reveals. And at the same time it acts like a big ear. Some of these webs can have a sensitive area up to 10,000 times the size of a spider. This network “ear” works so well, the study’s authors now report, that its effectiveness is “better than the acoustic response of all previously known eardrums.”
The new findings appeared on March 29 Proceedings of the National Academy of Sciences.
“It’s a super cool studio,” says Eileen Hebets. An archaeologist, she works at the University of Nebraska-Lincoln and was not involved in the research. She says the study “shows again how incredibly sophisticated spiders are.”
Ron Miles has been studying spiders and insects for 30 years. He is a mechanical engineer at Binghamton University in New York. In his work on developing better microphones, Miles studies animals that lack eardrums. “Typical microphones only measure air pressure,” he says. Like our eardrums. But sound also involves the pressure and movement of individual air particles. His team wanted to measure this air movement that monitors pressure changes.
For their new study, he and his team worked with bridge spiders. These animals build large, round (shaped) nets and then hang out in the center while waiting for their net to catch their meal.
Sound travels through the air in waves. In a previous study, Miles was part of a team that discovered that one strand of spider silk vibrates with moving air. This has led researchers to question whether silk could act as an elongated eardrum. Being able to listen for prey or - more importantly - predators is approaching could help spiders survive.
A new kind of hearing test
To test this, they collected 60 bridge spiders. In the laboratory, they placed each in its own container and gave it a square frame of 30 centimeters (12 inches) in which a net can be built. The researchers then took individual spiders on their webs to a separate room. Its walls were covered with thick, triangular pieces of foam. They absorb sound and prevent any echo from interfering with their study.
The team directed the speaker towards the spider web. Sometimes that speaker was directly in front of the net at a distance of three meters (10 feet). The second time was to the right or left of the net at an angle of 45 degrees. The videos captured the spider at rest and while it was exposed to a ton of five seconds. Some tones mimicked the sounds of ordinary prey, such as crickets. Others may be associated with an approaching predator. During one trial, the spider experienced only one tone. During the experiment, he heard tones at different frequencies and volumes.
Spiders responded to tones by squatting, flattening their bodies, lifting their front legs or turning to the side. When sounds were heard from the side, the spiders turned in the direction of the speakers. When they squatted or stretched, they moved strands of silk, which may have changed the way they detected vibrations.
https://www.youtube.com/watch?v=PIrotdSIkG4
It is possible that spiders have eardrums that have not yet been discovered. To test this, the team placed a small speaker just two millimeters - roughly the thickness of a coin - away from the grid. The speaker was five inches (two inches) away from the spider. Sound does not travel well through the air. By the time he reached the spider, he would have been very quiet. But the sound travels well through the spider’s silk.
When the researchers played a tone, the spiders responded, although any inner eardrum could not pick up the sound. This shows that spiders did not listen to sound like us. Instead, they collected vibrations from their networks.
Drawing inspiration from nature
“We usually think spiders can’t hear like us,” says Trinity Walls. She is a behavioral ecologist at the University of California, Berkeley, who did not participate in the study. Spiders seem to build their own “ears” of silk and modify them with body movements. “Let’s hope we as humans can learn from their techniques and maybe even use them to improve or correct people’s hearing loss,” she says.
In fact, Miles and his team hope to use their new discoveries to re-imagine how microphones work. “All microphones are designed to feel only pressure,” he says. They “completely ignore the ability to feel the movement of air.” He hopes to create microphones that can also sense the small flow of air in the sound field. This airflow could “indicate the direction to the sound source,” Miles explains. Knowing where unwanted sounds come from helps us figure out how to get rid of them [noise]. ”
“Much more needs to be done to understand what sounds mean to spiders,” Miles added. “Now that we know spiders can use their web to hear.”
Miles encourages curious teenagers to pay attention to what surrounds them. “Sometimes the things we see every day,” he says - like a spider’s web - can contain fascinating mysteries that you can unravel through careful research.