Spiders use their web like a speaker to boost their hearing, scientists say

Reasearchers found orb-weaving spiders can respond to sound levels as low as 68 decibels, Emily Atkinson reports

(Jee & Rani Nature Photography)

A groundbreaking study has found that orb-weaving spiders, made famous by the children’s book Charlotte’s Web, can use webs to help with hearing.

Researchers from the Department of Mechanical Engineering at Binghamton University’s Thomas J. Watson College of Engineering and Applied Science have uncovered evidence that suggests spiders can capture sounds using their webs, as well as prey.

Although it is widely known that spiders respond when something vibrates their web, the study, published in the journal Proceedings of the National Academy of Sciences, shows for the first time that spiders turned, crouched or flattened out in response to sounds in the air.

Professor Ron Miles, who has been studying the issue for 30 years, said the findings could potentially give way to designing extremely sensitive bio-inspired microphones for use in hearing aids and mobile phones.

According to the research team, 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.

Professor Miles, whose previous research has led to the invention of novel microphone designs based on hearing in insects, said: “The spider is really a natural demonstration that this is a viable way to sense sound using viscous forces in the air on thin fibres.

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

They are able to detect tiny movements and vibrations through sensory organs on their tarsal claws at the tips of their legs, which they use to grasp their webs.

Orb-weavers 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.

The team collected orb-weaving spiders from the windows around the campus at Binghamton University. They then had them spin a web inside a rectangular frame so they could position it where they wanted in the university’s anechoic chamber - a completely soundproof room.

The researchers began by using pure tone sound three metres away at different sound levels to see if the spiders responded or not.

They found that the orb-weavers can respond to sound levels as low as 68 decibels - the level of a normal conversation. For louder sounds, they uncovered even more behaviours.

The spiders can also tell the sound’s incoming direction with 100 per cent accuracy.

In a bid to better understand the spiders’ hearing mechanism, the researchers used laser vibrometry and measured over 1,000 locations on a natural spider web, with the spider sitting in the centre.

They found that the webs move with sound almost at maximum physical efficiency across an ultra-wide frequency range.

Professor Miles said: “Of course, the real question is, if the web is moving like that, does the spider hear using it? That’s a hard question to answer.”

Junpeng Lai, a doctoral student, added: “There could even be a hidden ear within the spider body that we don’t know about.”

The researchers also placed a mini speaker near the spider, which allowed them to conclude that the sound was picked up along the web more than in the air - proving that spiders could use the web to hear.

They 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.

In employing this external structure to hear, the spider may be able to customise it to hear different sorts of sounds, the study found.

Mr Lai admitted he was afraid of spiders when he began working on the project.

He said: “I’ve been afraid of spiders all my life, because of their alien looks and hairy legs.

“But the more I worked with spiders, the more amazing I found them. I’m really starting to appreciate them.”