While studying the acoustic properties of spider silk, researchers came across an interesting discovery: spiders can hear without ears.
Researchers in the US have discovered that spiders can use their webs to ‘hear’ sounds, extending their auditory sensing surface to up to 10,000 times their body size.
While most animals have ears containing ear drums that pick up on sounds and help them navigate and avoid predators, spiders are known to not have a separate organ for experiencing auditory senses.
But researchers from Binghamton University and Cornell University in New York made a surprise discovery while studying the acoustic properties of spiderwebs: that orb-weaver spiders can use their webs as reconfigurable antennas and ‘hear’ sounds around them.
Orb-weaver spiders are a special class of arachnid that can create orb-like circular webs in gardens and homes made of proteinaceous spider silk, generally to catch prey.
Ronald Miles, a professor of mechanical engineering at Binghamton University, along with colleagues Ronald Hoy, Jian Zhou and Junpeng Lai, decided to study these spiders after finding spider silk to be responsive to sound.
“The question came up that if spider silk responds to sound so well, maybe spiders can use their silk to hear,” said Miles in a video explaining the discovery. “Maybe the spider could use that silk motion as it moves in response to sound and hear with the web.”
The team, which published its study in the journal PNAS last week, exposed 72 spiders in sealed lab chambers to acoustic tones emitted from varying distances and angles to the webs and recorded the spiders’ reactions.
They found that the spiders were able to detect and respond to tones emitted from speakers placed up to three metres away at oblique angles to the web and rapidly turn towards the source.
A technique called Doppler vibrometry was used to measure the webs’ motion induced by the test tones. Researchers found that webs followed the movement of air particles with “high fidelity and efficiency, exceeding the acoustic responsiveness of eardrums”.
Lai, who measured the web’s responsiveness to sound, said that the study “opens new perspectives for other researchers, especially biologists”. The results enrich scientific understanding of spider silk and could inform the design of acoustic flow detectors.
“Understanding exactly what it means for the spider is kind of another question for someone else to answer,” added Miles.
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