These Spiders Use Their Webs Like Huge Silky Ears

These Spiders Use Their Webs Like Huge Silky Ears
Credit: Mateusz Kropiwnicki/Getty Images

A study of orb-weaving spiders shows that the arachnids’ webs pick up a range of sounds–and they are always “listening” for vibrations coming in over them.

Karen Hopkin: This is Scientific American’s 60-Second Science. I’m Karen Hopkin.

Some things are SO adorable, we say they’re cute as a bug’s ear. Of course, bugs do not have ears. A new study has shown that orb-weaving Spiders can detect sounds using their webs, according to a new study. The findings are unfurled in the Proceedings of the National Academy of Sciences.

Ron Hoy: Any animal that makes sounds is likely to have an ear.

Hopkin: Ron Hoy studies neurobiology and behavior at Cornell University in Ithaca.

Hoy: …ranging all the way from tiny crickets, and flies that are even smaller than crickets, all the way through to humans of course.

Ron Miles: It’s also pretty interesting that a great many animals don’t have eardrums. They still hear.

Hopkin: That’s Ron Miles.

Miles: The two Rons, here.

Hopkin: Ron Miles, who’s been collaborating with Ron Hoy for 30 years, is an engineer at Binghamton University…

Miles: …an hour’s drive away from Cornell.

Hopkin: Critters lacking eardrums receive audio input very fine hairs.

Miles: If you look at spiders and insects, they’re covered with hairs.

Hopkin: Because these whispy little filaments can float freely in the breeze, they’re great at sensing the air currents that comprise sound waves.

Miles: Since we knew that so many animals like small insects and spiders have hairs that can sense sound, … we were kind of wondering how would you make something that could sense sound the way that some of these small animals do.

Hopkin: A possibility appeared during an afternoon stroll.

Miles: My graduate student, Jian Zhou, was walking in our campus nature preserve one day and he noticed when the wind blew, if you look at a spider web, it moves with the wind. He thought that a fine spiderweb or spider silk could be used as a sound sensor.

Hopkin: To find out, the researchers coaxed a spider into giving them a bit of silk…

Miles: … and we played sound at a little strand of spider silk and found that when the silk is very thin, it moves with the air in a sound field amazingly well… over a wide range of frequencies, from 1 hz to 50 khz. We knew that spider silk was an ideal sound sensor.

Hopkin: That was eye-opening for the researchers…but is it ear-tickling for the spiders?

Miles: So we set out to try to figure out if the spiders were actually able to hear sound using their web. This was a difficult question to answer.

Hopkin: For one thing, they had to find a way to get a whole web into the special soundproof chamber in the basement of the lab building.

Miles: You know, spider webs are very delicate. It is not possible to go out into the woods and pick up a spiderweb and take it home. It can be attached to other things. It’s not easy to get it back intact.

Hopkin: Especially those made by the industrious orb-weavers…spiders like the title character in Charlotte’s Web.

Hoy: We’re talking about quite a spectacular web. It’s a wheel-shaped web that runs throughout upstate New York. If you walk through any field, either you’ll walk through it or you’ll see it and try to avoid it because it’s too big. It can grow up to a meter or even a yard in size.

Hopkin: So Jian Zhou and fellow student Junpeng Lai came up with a way to get custom-made webs custom to go.

Miles: What they did is make a little wooden frame… kind of the size of a decent sized picture frame…and they placed this frame on the windows of our building.

Hopkin: The lights in the building attracted bugs…and the bugs attracted spiders.

Miles: So…the spiders built their webs on the frames. My students would then go to the frames and hijack the spiders. They would then take the frames to their classroom and place them in the chamber intact.

Hopkin: Now, how can you tell whether a web functions as an arachnid hearing aid? You can check the brain of the spider to determine if it is functioning as an arachnid hearing aid.

Hoy: My lab, the neurophysiologists, made some recordings from the nervous system sensory system that showed that indeed you get an acoustic response in the nerves to sound…coming from a speaker a little more than a meter away.

Hopkin: But even more revealing was how the spiders acted.

Hoy: To very loud sounds, you could get a strong response…the spider would either flatten out or it might actually crouch. It’s actually hunkering down. This is a sign that there is an alarm response, according to a biologist.

Hopkin: And when serenaded with sounds that are maybe 10 decibels or 100 times softer…

Hoy: Without changing its body posture or making any other movements, it might simply raise its front two legs off of the web.

Hopkin: That leg lift, says Hoy…

Hoy: …is a spider’s way of maybe putting two more sensors out there to see what’s coming. We don’t yet know this. That response to a very soft stimulus could be the spider’s response to the question, “I know something is out there, but I need to get more information.” This was the demonstration that proved that spiders can hear sound.

Hopkin: This filamentous approach to acoustics could someday change the way we make microphones…and take webcasting to a whole new level.

For Scientific American’s 60 Second Science, I’m Karen Hopkin.

[The above text is a transcript of this podcast. ]

ABOUT THE AUTHOR(S)

    Karen Hopkin is a freelance science writer in Somerville, Mass. She holds a doctorate in biochemistry and is a contributor to Scientific American‘s 60-Second Science podcasts.

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