Macroscopic Solutions

Turns out spiders can hear you from across the room

Total nightmare.

FIONA MACDONALD
14 OCT 2016
 

A new study has just revealed that spiders are even more impressive - or terrifying, depending on your point of view - than we'd ever imagined.

Arachnids don't have ears, but it turns out spiders can hear you talking from metres away - despite the fact that many researchers previously assumed they couldn't hear at all.

 

"Surprisingly, we found that they also possess an acute sense of hearing," lead researcher Paul Shamble from Cornell University told Hannah Devlin from The Guardian.

"They can hear sounds at distances much farther away than previously thought, even though they lack ears with the eardrums typical of most animals with long-distance hearing."

Instead of eardrums, spiders use the tiny, sensitive hairs on their legs to detect noises, the new study suggests.

Although it was previously known that spiders' leg hairs were sensitive to airborne vibrations - such as sound waves - the assumption was that this only extended to sounds around a spider's body length or a few centimetres away.

And no one had thought the arachnids were then interpreting those vibrations into neural activity - which would mean they're actually ‘hearing’ those sound waves, rather than just sensing them.

But now new research based on spider brain patterns shows they can actually hear humans talking and clapping from up to 5 metres away. 

 

Which is... great news... If you're listening, spider friends, I'm really happy for you :|

The research was performed on small North American jumping spiders, Phidippus audax, and the coolest part is that the discovery was made purely by accident.

Shamble and his team were making neural recordings of the spiders' brains to find out how they processed visual information. 

"One day, [co-researcher Gil Menda] was setting up one of these experiments and started recording from an area deeper in the brain than we usually focused on," Shamble told Maarten Rikken over at Research Gate

"As he moved away from the spider, his chair squeaked across the floor of the lab. The way we do neural recordings, we set up a speaker so that you can hear when neurons fire - they make this really distinct 'pop' sound - and when Gil's chair squeaked, the neuron we were recording from started popping. He did it again, and the neuron fired again."

That was surprising enough, but Menda and Shamble then started clapping at increasing distances to see when the spider would stop registering it. They got up to 5 metres away, and the spider was still responding.

"Based on everything they knew it shouldn't have been possible, but there it was," said Menda. "It was just the beginning of months and years of work, but it was an incredible start."

To figure out exactly how the spiders were hearing them, the team then placed water droplets on their legs to dull the vibrations of the hairs.

When they did this, the auditory neurons in the brain stopped firing in response to sounds, suggesting that the spiders couldn't hear anymore.

Further experiments confirmed that, although the spiders responded to claps, they were most sensitive to low frequencies (about 80-130 Hz), which is around the frequency of the wingbeats of parasitoid wasps, which prey on jumping spiders. It's also around the pitch of a deep male voice.

But even though the spiders have acute hearing, it wouldn't necessarily sound the way it does to us, due to how their brains process it. 

"It probably sounds like a really bad phone connection," Shamble told The Guardian. "They probably can tell that you’re talking from across the room, but they’re certainly not listening to you."

The team is now investigating whether other spider species, such as wolf spider and fishing spiders, have the same ability.

Their research has been published in Current Biology.

(Now let's all just sneak out of the room really quietly and hope they don't hear us.)

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