Spiders use webs to extend their hearing

Date:
March 29, 2022
Source:
Binghamton University
Summary:
A newly published study of orb-weaving spiders has yielded some
extraordinary results: The spiders are using their webs as extended
auditory arrays to capture sounds, possibly giving spiders advanced
warning of incoming prey or predators.



FULL STORY ========================================================================== Everyone knows that humans and most other vertebrate species hear using eardrums that turn soundwave pressure into signals for our brains. But
what about smaller animals like insects and arthropods? Can they detect
sounds? And if so, how?

========================================================================== Distinguished Professor Ron Miles, a Department of Mechanical Engineering faculty member at Binghamton University's Thomas J. Watson College of Engineering and Applied Science, has been exploring that question for more
than three decades, in a quest to revolutionize microphone technology.

A newly published study of orb-weaving spiders -- the species featured
in the classic children's book "Charlotte's Web" -- has yielded some extraordinary results: The spiders are using their webs as extended
auditory arrays to capture sounds, possibly giving spiders advanced
warning of incoming prey or predators.

The paper, "Outsourced Hearing in an Orb-Weaving Spider that Uses its
Web as an Auditory Sensor," published March 29 in the Proceedings of the National Academy of Sciences, provides the first evidence that a spider
can outsource hearing to its web.

It is well-known that spiders respond when something vibrates their
webs, such as potential prey. In these new experiments, researchers for
the first time show that spiders turned, crouched or flattened out in
response to sounds in the air.

The study is the latest collaboration between Miles and Ron Hoy, a
biology professor from Cornell, and it has implications for designing
extremely sensitive bio-inspired microphones for use in hearing aids
and cell phones.



==========================================================================
Jian Zhou, who earned his PhD in Miles' lab and is doing postdoctoral
research at the Argonne National Laboratory, and Junpeng Lai, a current
PhD student in Miles' lab, are co-first authors. Miles, Hoy and Associate Professor Carol I.

Miles from the Harpur College of Arts and Sciences' Department of
Biological Sciences at Binghamton are also authors for this study. Grants
from the National Institutes of Health to Ron Miles funded the research.

A single strand of spider silk is so thin and sensitive that it can
detect the movement of vibrating air particles that make up a soundwave,
which is different from how eardrums work. Ron Miles' previous research
has led to the invention of novel microphone designs that are based on
hearing in insects.

"The spider is really a natural demonstration that this is a viable
way to sense sound using viscous forces in the air on thin fibers," he
said. "If it works in nature, maybe we should have a closer look at it." Spiders can detect miniscule movements and vibrations through sensory
organs on their tarsal claws at the tips 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 area
that is up to 10,000 times greater than 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 windows around campus, they had the spiders
spin a web inside a rectangular frame so they could position it where
they wanted.



==========================================================================
The team began by using pure tone sound 3 meters away at different sound
levels to see if the spiders responded or not. Surprisingly, they found
spiders can respond to sound levels as low as 68 decibels. For louder
sound, they found even more types of behaviors.

They then placed the sound source at a 45-degree angle, to see if the
spiders behaved differently. They found that not only are the spiders localizing the sound source, but they can tell the sound incoming
direction with 100% accuracy.

To better understand the spider-hearing mechanism, the researchers
used laser vibrometry and measured over one thousand locations on a
natural spider web, with the spider sitting in the center under the
sound field. The result showed that the web moves with sound almost at
maximum physical efficiency across an ultra-wide frequency range.

"Of course, the real question is, if the web is moving like that, does
the spider hear using it?" Miles said. "That's a hard question to answer."
Lai added: "There could even be a hidden ear within the spider body that
we don't know about." So the team placed a mini-speaker 5 centimeters
away from the center of the web where the spider sits, and 2 millimeters
away from the web plane -- close but not touching the web. This allows the sound to travel to the spider both through air and through the web. The researchers found that the soundwave from the mini-speaker died out significantly as it traveled through the air, but it propagated readily
through the web with little attenuation. The sound level was still at
around 68 decibels when it reached the spider. The behavior data showed
that four out of 12 spiders responded to this web-borne signal.

Those reactions proved that the spiders could hear through the webs,
and Lai was thrilled when that happened: "I've been working on this
research for five years. That's a long time, and it's great to see
all these efforts will become something that everybody can read."
The researchers also found that, by crouching and stretching, spiders may
be changing the tension of the silk strands, thereby tuning them to pick
up different frequencies. By using this external structure to hear, the
spider could be able to customize it to hear different sorts of sounds.

Future experiments may investigate how spiders make use of the sound
they can detect using their web. Additionally, the team would like to
test whether other types of web-weaving spiders also use their silk to outsource their hearing.

"It's reasonable to guess that a similar spider on a similar web would
respond in a similar way," Ron Miles said. "But we can't draw any
conclusions about that, since we tested a certain kind of spider that
happens to be pretty common." Lai admitted he had no idea he would
be working with spiders when he came to Binghamton as a mechanical
engineering PhD student.

"I've been afraid of spiders all my life, because of their alien looks and hairy legs!" he said with a laugh. "But the more I worked with spiders,
the more amazing I found them. I'm really starting to appreciate them."
Video: https://youtu.be/PIrotdSIxG4

========================================================================== Story Source: Materials provided by Binghamton_University. Original
written by Chris Kocher.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jian Zhou, Junpeng Lai, Gil Menda, Jay A. Stafstrom, Carol I. Miles,
Ronald R. Hoy, Ronald N. Miles. Outsourced hearing in an orb-weaving
spider that uses its web as an auditory sensor. Proceedings
of the National Academy of Sciences, 2022; 119 (14) DOI:
10.1073/pnas.2122789119 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220329114714.htm

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