Spiders don’t have ears, but they can enhance their “hearing” with giant webs

(ORDO NEWS) — The web is essential for grabbing food, but it can also be used as a giant hearing aid for the arachnids that weave it, according to a new study.

Spiders do not have ears, but they can “hear” vibrations through their legs. When prey or predators are on the move, the transmission of these vibrations through the web can be invaluable, according to the authors of the new study, as the web is sometimes 10,000 times the size of the creatures themselves.

The researchers used a collection of weaver spiders, known for their large webs, for experiments, having them weave webs in rectangular frames in the lab, which were then subjected to a series of tests.

“We found that the weaver’s wheel-shaped web acts as an ultra-sensitive acoustic antenna to pick up the movements of air particles caused by sound,” the researchers write in their published paper.

A laser vibrometer was used to measure the response of gossamer silk to music in an anechoic chamber, a room designed to minimize the reflection of sound waves. The measurements showed that the web moved almost in unison with the sound, potentially picking up the sound as it appeared.

Sounds of different frequencies and from different directions were tested with the webs, which then received corresponding responses from the spiders – they usually turned, squatted or straightened in response. In the case of directional sound, the spiders oriented in the direction from which the sound was coming.

Further experiments with miniature speakers placed close to the edge of the web showed that sound traveled farther through the web than through air, and some spiders responded to vibration even when the sound did not reach the spiders through the air.

It’s less clear what the spiders do with this information.

We know that spiders are able to hunt in packs, for example, through the vibration of the web transmitted through sensory organs on the tarsal claws at the tips of the spider’s legs. In this case, they are clearly responding to something when struck by sound waves, but further research will be needed to find out how spiders process this information.

“There may even be a hidden ear in the spider’s body that we don’t yet know about,” says Junpeng Lai, a mechanical engineer at Binghamton University in New York.

The new study builds on previous research on how webs respond to sound and music, but how silk threads respond to sound waves is different from how eardrums behave.

Humans and most other vertebrate species have eardrums that convert sound wave pressure into electrical signals, which are then decoded in our brains. Insects and arthropods (including spiders) do not have such eardrums, so the web can serve as a replacement.

With their movements in response to sounds, spiders can even tune the strands of the web to pick up different sound frequencies. Researchers have many potential avenues to explore based on this latest study – and that includes possible improvements to audio hardware that could benefit from some natural inspiration.

“The spider is indeed a natural demonstration that it is a viable way to perceive sound using viscous forces in air on thin fibers,” says mechanical engineer Ron Miles of Binghamton University.

“If it works in nature, maybe we should take a closer look at it.”

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