Everybody thought the tiny arachnids lack sensitive hearing past a couple body lengths away but it turns out spider can even hear you from across the room. Sorry, arachnophobes, spiders just got a lot scarier.
Humans, like most vertebrates, hear by converting the vibrations carried by acoustic pressure waves into sound via our eardrums. But spiders don't have ears and instead rely on tiny hairs that litter their legs to transmit sound vibrations. The assumption used to be, however, that they can only sense noises extending a couple of body lengths away or a few centimeters. Moreover, no one actually thought that these vibrations actually get converted into neural signals we all know as hearing.
Turns out we've underestimated spider senses, according to Gil Menda and Paul Shamble from Cornell University. The two were working on a new method that enabled them to read neural signals inside a spider's minuscule brain. Because of the way their experiment was set up, a popping sound was made by a computer whenever spider neurons fired which corresponded to a stimulus. But when one of them moved a chair, a sound popped. When they clapped their hands from across the room, they were met by a pop again. Their minds were immediately filled with possibilities and a new experiment was born.
Jumping spiders were placed in a special acoustic arena designed to absorb most sound reflections or echoes. Menda and Shamble then played all sorts of frequencies. One of them was the familiar frequencies made by a wasp when it flaps its wings, which the spiders responded to by freezing -- a typical fear response. The other frequencies were also met by a response and high-speed cameras demonstrated that these were picked up by sensory hairs that shook back and forth.
Even from 16 feet (5 meters) away the spiders could still respond to the frequencies.
“This is real, and it's not only with jumping spiders,” said Menda, who now plans on replicating the experiment on other spider species.
Don't expect their hearing to be too clear though, say the researchers who published their work in Current Biology.
"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 findings have implications for animal research. Scientists who studied arachnid behavior but ignored their sense of hearing, for instance, could be missing some important cues. The findings could also help us understand how spider hearing evolved, but could also lead to new technologies. Things that come to mind are sensitive micro-robots or a new generation of microphones and hearing aids that work on the same principle that enables the spider's astonishing hearing.
"They can hear everything we do,” said Menda, who used to bring a wary eye to “Spider-Man” movie sessions with his kids. “I used to laugh at [the movies], because spiders can't hear sounds. Well, guess what? They can.”