Spiders Routinely Use Webs To Expand Their Hearing Capabilities: Here's How

Researchers from Binghamton University¡¯s Thomas J. Watson College of Engineering and Applied Science have discovered in their study that spiders use their webs as extended auditory arrays to capture sounds.

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The study looked at orb-weaving spiders in particular. It is already established that spiders respond when something vibrates their webs -- this could either be a potential prey or even a potential danger.

The novel study however, has for the first time shown that spiders turned, flattened or crouched in response to sounds in the air. The strand of silk that makes the spider¡¯s web is so thin and sensitive that it is able to capture movement of vibrating air particles that form a soundwave.

Researchers found that spiders were able to detect even the slightest movements and vibrations through sensory organs on their tarsal claws at the tips of their legs, that they use to grab onto the web.

Orb-weaver spiders in particular are known for their large webs, that form a sort of acoustic antennae with a sound-sensitive surface area that¡¯s 10,000 times greater than the spider itself.

Researchers in the study made use of Binghamton University¡¯s anechoic chamber -- a fully soundproof room. Here they had the spiders to weave a web inside a rectangular frame. Post this, they began testing pure tone sound three metres away at varied sound levels to see if spiders responded to it.

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Researchers found that spiders were prompt to respond to sound levels as low as 68 decibels. When the sound was made louder, they found even more types of behaviours.

To take things to the next level, they placed the source of the sound at a 45-degree angle. They found that not only are the spiders able to locate the sound, they're able to do it with 100 percent accuracy.

To dig deeper on the workings of this mechanism, the researchers used laser vibrometry and measured over one thousand locations on a natural spider web. With the spider sitting in the centre under the sound field. Researchers saw that the web moved with sound almost at maximum physical efficiency across an ultra-wide frequency range.

They also placed a mini speaker 5 centimetres away form the centre of the web and 2 millimetres away from the web plane, making sure it didn't touch the web. This was to allow the sound to travel to the spider not just through web but also through air.

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They saw that the soundwave from the mini speaker died out significantly as it travelled through air, but propelled steadily through the web with little hurdles. The sound level was still at around 68 decibels when it reached the spider. Out of 12 spiders, four responded to this signal.

Researchers claim that when spiders crouch, stretch they alter the tension in the web that actually tunes the web to hear different frequencies.

Future research could help decipher how spiders use the sounds they hear using their web. Researchers also wish to test if other web-weaving spiders use silk for hearing.

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