Spiders use webs to extend their hearing: study

A spider web glistens in the morning dew as the sun rises to an early morning fog over a farmers field in Ottawa Tuesday July 31, 2001.(CP PHOTO/Tom Hanson)

A new study, with three decades in the making, has revealed that spiders are not only using their webs to hear but to tell where sound is coming from.

The research, which looked at orb-weaving spiders specifically, suggests that the spiders use their webs as extended auditory arrays to capture sounds, which might provide them with early notice of approaching prey or predators.

The study is the latest collaboration between Ron Miles, a Mechanical Engineering faculty member at Binghamton University and Ron Hoy, a biology professor from Cornell, and has implications for designing sensitive bio-inspired microphones in hearing aids and cell phones.

Spiders are well-known for reacting to vibrations in their webs, such as possible prey.

But according to the observations of this latest study, spiders also turn, crouch or flatten themselves in reaction to noises in the air.

"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," Miles said.

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

Miles' previous research has led to the invention of novel microphone designs that are based on hearing in insects.

Miles and his colleagues at Binghamton University have continued their research into how spider silk can detect sound in the hopes of producing more sophisticated microphones for use in anything from hearing aids to cell phones.

They recently captured orb-weaving spiders from around campus and had them build webs within moveable rectangular frames as part of their newest experiment.

The scientists used pure tone sound from three metres away at various sound levels to check if the spiders responded.

Surprisingly, they discovered that spiders can detect sounds as low as 68 decibels.

The sound source was then angled at a 45-degree angle to test if the spiders responded differently. They discovered that the spiders can not only locate the sound source, but they can also accurately predict the sound's upcoming direction.

The researchers then employed laser vibrometry to measure over one thousand sites on a natural spider web, with the spider sitting in the middle under the sound field, to better understand the spider’s hearing process.

The findings revealed that the web moves with sound at a nearly maximum physical efficiency across a wide frequency range.

"Of course, the real question is, if the web is moving like that, does the spider hear using it?" Miles said in a release. "That's a hard question to answer."

To answer this question, the scientists devised a creative experiment that involved placing a small speaker two millimetres away from the web plane and five centimetres away from the web's centre, where the spider resides.

This meant that sound reached the spider both through the air, where it quickly faded out, and through its webbing, reaching the spider at levels of around 68 decibels, proving that the spiders could hear through the webs.

"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,” said Junpeng Lai in a release, who co-authored the story.

Future experiments may investigate how spiders make use of the sound they can detect using their web.

The researchers also want to see if other species of web-weaving spiders utilise their silk to outsource their hearing.