Karen Hopkins: It’s science in 60 seconds from Scientific American. I am Karen Hopkin.
Some things are SO adorable, we say they’re cute as a bug ear. Of course, insects don’t have ears. But a new study shows that orb-weaving spiders can use their webs to detect sounds. The discoveries are unveiled in the Proceedings of the National Academy of Sciences.
Ron Hoy: Any animal that makes sounds is likely to have an ear.
Hopkins: Ron Hoy studies neurobiology and behavior at Cornell University in Ithaca.
Hi : … ranging from small crickets to flies even smaller than crickets, to humans of course.
Ron Miles: It is also interesting to note that a large number of animals do not have eardrums. But they still hear.
Hopkins: It’s Ron Miles.
Miles: The two Rons here.
Hopkins: Ron Mileswho collaborated with Ron Hoy for 30 years, is an engineer at the University of Binghamton…
Miles: …an hour’s drive from Cornell.
Hopkins: Creatures without eardrums receive very fine hairs as audio input.
Miles: If you look at spiders and insects, they are covered in hair.
Hopkins: Because these little hissing filaments can float freely in the breeze, they’re great for detecting the air currents that make up sound waves.
Miles: Since we knew that so many animals like small insects and spiders have hairs that can sense sound, … we were wondering how to make something that could sense sound like some of these little animals do.
Hopkins: A possibility appeared during an afternoon stroll.
Miles: My graduate student, Jian Zhou, was walking around our campus nature reserve one day, and he noticed that when the wind blows, if you look at a spider web, it moves with the wind. And he thought maybe a thin spider web or spider silk could act as a sound sensor.
Hopkins: To find out, the researchers persuaded a spider to give them some silk…
Miles: …and we played sound on a small strand of spider silk and found that when the silk is very thin, it moves incredibly well with the air in a sound field…over a wide frequency range, from 1Hz at 50 kHz. We knew then that spider silk was somehow an ideal and perfect sound-catcher.
Hopkins: This was eye-opening for researchers… but does it tickle spiders’ ears?
Miles: So we tried to determine if spiders were actually able to hear sound using their web. And that was a difficult question to answer.
Hopkins: On the one hand, they had to find a way to introduce an entire canvas into the special soundproof chamber in the basement of the laboratory building.
Miles: You know, cobwebs are very delicate. You can’t go out into the woods and find a spider’s web, grab it, and bring it home. It’s attached to things. And it is not easy to recover it intact.
Hopkins: Especially those made by the industrious orb-weavers…spiders like the main character in Charlotte’s Web.
Hi : We are talking about a rather spectacular web. It’s this wheel-like web that circles upstate New York…if you walk through a field, you’ll either walk through one or see it and avoid it because it’s big. It can reach the size of a meter or a meter in diameter.
Hopkins: Jian Zhou and his comrade Junpeng Lai therefore found a way to obtain custom-made canvases.
Miles: What they did was make a little wooden frame…kinda the size of a decent sized picture frame…and they put that frame on the windows of our building.
Hopkins: The lights in the building attracted insects…and insects attracted spiders.
Miles: So…the spiders built their webs on the frames. Then in the morning, my students would fetch the frames and basically hijack the spiders and pick them up and put the frame in the… intact chamber.
Hopkins: Now, how do you know if a web works as an arachnid hearing aid? One way is to keep an eye on the spider’s brain.
Hi : My lab, the neurophysiologists, made recordings of the sensory system of the nervous system that showed that indeed you get an acoustic response in the nerves to sound… coming from a loudspeaker a little over a meter away distance.
Hopkins: But even more telling was the way the spiders acted.
Hi : At very loud sounds you might get a loud response… the spider would flatten out or might even crouch. But it’s really squatting. It is indicative [to a biologist] an alarm response.
Hopkins: And when serenaded with sounds that are maybe 10 decibels or 100 times softer…
Hi : Without changing his body posture or making any other movements, he can simply lift his two front legs off the canvas.
Hopkins: That leg lift, says Hoy…
Hi : …is a spider’s way of maybe putting two more sensors in there to see what’s going on. We do not know yet. But this response to a very mild stimulus could simply be the spider’s reaction to “I know there’s something out there, I heard it, but I need more information.” So…it’s basically the demonstration that was needed to show that spiders can hear sound.
Hopkins: This stringy approach to acoustics could one day change the way we make microphones… and take webcast on a whole new level.
For Scientific American’s 60 Second Science, I’m Karen Hopkin.
[The above text is a transcript of this podcast.]