You might know them as silk weavers, web architects, insect exterminators, or maybe just miniature eight-legged monsters — so goes the versatile nature of spiders. But despite this already impressive resume, scientists might’ve found arachnids’ most fascinating talent yet: hearing without ears.
In a paper published Tuesday in the Proceedings of the National Academy of Sciences, researchers from Binghamton University discovered that orb-weaving spiders (like the one in Charlotte’s Web) can detect sound through minute vibrations on their spiderweb.
It’s a clever auditory outsourcing trick that might be precisely how the critters compensate for their lack of eardrums, which prevents them from “hearing” like us.
As humans, we rely on our eardrums to convert soundwave pressure into signals that our brain can comprehend, then, once our brain processes those signals, we learn what the sound is, where it’s coming from, how loud it is, and so on. Without eardrums, the world would be silent. Most other vertebrates hear this way too, but animals like insects and spiders don’t have such an auditory tool.
Over the years, studies have proven that spiders sort of hear with the teeny hairs on their crawly legs because the fuzz is sensitive toward nearby sound vibrations, but that’s pretty much as far as experts thought arachnid auditory senses go — until now, that is.
And, though the new study’s web-vibration finding is astonishing in itself, it also suggests something arguably even more jaw-dropping. Orb-weaving spiders might physically tune their spiderweb strings to zero-in on whichever tone they so desire.
The concept is akin to how we tune our car radio to find our favorite station — except, I’d assume spiders are more interested in the buzz of a bee, wing-flap of a dragonfly…or, maybe the scream of a human?
Either way, perhaps it’s time we add “radio engineer” to the intriguing spider skillset.
The outsourced hearing of orb-weaving spiders
For their new study, the researchers collected a bunch of orb-spiders from windows on the campus of Binghamton University, where the experiments were conducted.
They put each crawly subject into a rectangular frame within a soundproof room, and waited for the spiders to build their webby creations. After that, the team played sounds to see whether the spiders would listen in and react — they did, even to noise that was really (really) low in volume.
Then, to take things a step further, the team tried playing the sounds at different angles to see if the spiders could figure out where it was coming from — they did, and with a whopping 100% accuracy.
Sure enough, after analyzing the orb-weaving spiders’ webs, the researchers found that the delicate creations swiftly catching movements of nearby air particles, which were vibrating as a result of the sound waves. Thus, the team concluded that by standing on the vibrating strings, orb-weaving spiders can sense, or rather “hear,” sound.
Plus, the researchers found that while sensing the sounds, the spiders either crouched or stretched on the web. Though this behavior has been witnessed in the past, it didn’t have much reasoning. But with their new knowledge that spiderwebs have something to do with the spiders’ auditory perception, the team started connecting the dots.
It’s likely, they say, that spiders actively change the tension of strands by crouching, for instance, thereby customizing their web to tune-in to specific sounds like a radio.
Before making any major claims, however, the researchers wanted to address one last major caveat. “The real question is, if the web is moving like that, does the spider hear using it?” Ron Miles, a mechanical engineer at Binghamton University and co-author of the study, said in a statement. “That’s a hard question to answer.” To get around this, Miles and co-author Junpeng Lai, who’s a doctoral student in Miles’ lab, conducted a final experiment.
They used a mini-speaker to play sounds for the spiders that almost completely died down in volume before reaching the web, but continued strongly propagating through the webs’ strings as vibrations. In essence, this isolated the string vibration aspect from the actual, listenable sound aspect. Per the study, four out of 12 spiders still responded to even the extremely weak signal, meaning they could feel the vibrations on the web itself and ruling out the caveat.
Going forward, Miles urges that future research should look into whether other types of spiders partake in the same behavior, though saying “it’s reasonable to guess that a similar spider on a similar web would respond in the same way.”
And, even farther down the line, he believes these findings could inform the way we design microphones, hearing aids and cell-phones. “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.”