Some spiders can pick up sounds in the air using their webs as acoustic antennae, and because the spider silk responds so precisely to vibrating air molecules, the webs may act as the most sensitive 鈥渆ardrums鈥� in the natural world.
We already know that spiders can detect prey tangled in their webs by sensing vibrations in the silk using touch organs around their leg joints.
Now, at the Argonne National Laboratory in Illinois and his colleagues have found evidence that bridge spiders (Larinioides sclopetarius) can use their webs to sense sounds travelling through the air from several metres away. The team placed 60 bridge spiders in glass chambers containing wooden frames on which the spiders wove their circular webs.
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The group then played sounds with a frequency of 200 hertz 鈥� similar to those made by buzzing insects 鈥� onto each spider and its web for 3 seconds, from loudspeakers located 3 metres away. Over the next few seconds, 90 per cent of spiders responded by either crouching, lying flat, lifting their forelegs or turning slightly, suggesting that they had detected the distant sounds.
By projecting sounds either from the left or the right of the webs, the team found that some of the spiders could even sense exactly where the noises were coming from. Five out of 12 tested spiders pivoted towards the direction of the sound source, while the others stayed put.
The team explored if webs could act as acoustic sensors by playing sounds with frequencies ranging from 100 to 10,000 Hz onto the webs. Using a laser to map the nanoscale movements of the webs as sounds were projected onto them revealed that the silk strands could move at the same speed as the air molecules immediately around them, transmitting the full array of frequencies tested. This makes the webs far more sensitive than all known animal eardrums, which as membranes respond instead to bulk sound waves in the air.
The frequency range sensitivity means the webs can detect sounds made by chirping crickets, birds and the buzzing wings of insects.
To rule out the possibility that the spiders detected sounds from the air using an unknown body part, the team used a tiny speaker to direct sound onto just one small area of each spider鈥檚 web, away from where the spider sat.
These sounds were weak enough to be undetectable in the air once they reached the spider鈥檚 body, but a third of spiders still crouched in response to the vibrations, suggesting that they could hear through their webs alone.
The team speculate that bridge spiders, and other spider species, may even tune their web design to filter out local background noise such as the wind 鈥� although more research would be needed to determine that.
Reference: 产颈辞搁虫颈惫,听
