There’s nothing worse than a noisy neighbor when you are trying to have a nice meal — even if that meal consists of liquefying the insides of your prey before sucking them back up.
New research shows that some spiders living in cities somehow weave soundproofing designs into the fabric of their webs to manage unwanted noise, which can make it difficult for them to find prey and detect mates.
“These spiders have come up with an incredible solution — they are able to use their webs as both a hearing aid and hearing plug,” said Eileen Hebets, a biologist at the University of Nebraska-Lincoln and an author of a paper led by Brandi Pessman, a postdoctoral research associate at the university.
Funnel-web spiders are widespread in North America. Quarter-size with legs outstretched, these spiders attach their webs to everything, whether rocks and grass or human objects. They weave a kind of funnel into their webs where they typically hide from predators. Their silk isn’t sticky, so they rely on speed and ambush. After sensing prey on their webs, they burst out and attack, injecting their victims with venom and then liquefying their insides for easy digestion.
Spiders don’t have ears like humans, so they don’t necessarily hear things in the traditional way. But sound produces vibrations that travel through the ground and into their webs via silk strands.
“They really rely on those accurate vibrations to determine where the prey is, what the prey is and whether to attack,” Dr. Pessman said.
Beth Mortimer, a biologist who studies noise pollution at the University of Oxford and was not involved in the research, added, “The vibration sense tends to be the forgotten sense in the natural world.” The species is at home building webs in both cities and rural areas. And Dr. Pessman began wondering whether noise pollution might annoy the spiders enough to alter their web-weaving strategies.
In a study published last week in the journal Current Biology, Dr. Pessman and Dr. Hebets rounded up arachnid city slickers and country bumpkins and took them to a laboratory. They placed each spider in a container with a speaker at the bottom that played either loud or quiet white noise for four days to the spider.
The researchers then analyzed the webs that each spider built by sending measured vibrations at different points.
Dr. Hebets and Dr. Pessman didn’t find much difference in the way the webs of city spiders and farm spiders transmitted vibrations when they played the quiet noise.
When they played loud noise to the city spiders, they found that their webs were less sensitive, transmitting fewer vibrations to the funnel. “Their webs were essentially quieter,” Dr. Pessman said. The researchers weren’t sure how the webs differed structurally, but it Dr. Pessman said it seemed clear that “they are cutting down on the constant noise they are getting close to where they are sitting.”
Conversely, when the country spiders heard loud noise, they built webs that were more sensitive. The researchers speculated that they weren’t used to that kind of racket and were desperately trying to sense incoming prey. It’s like turning up your television as a lawn mower passes close to your window.
The city spiders, on the other hand, essentially padded their walls because they were sick of it all — an adaptation that could put them at a disadvantage for hearing prey or potential mates, which also use vibrations to communicate their availability. But that may help the animals save their energy and not react to every urban sound they detect.
“If you’ve got masking noise, it means you’ll be less likely to detect the small items that come into your web,” said Dr. Mortimer, who said the study “was done really well.”
The research highlights the sophistication of spiders, Dr. Hebets said, as they have come up with a solution for finding food and mates despite their big city problems.
“While animal sensory systems can, and do, certainly adapt over evolutionary time to changing environmental conditions, this takes time,” Dr. Hebets said. “Behavioral changes, however, can be immediate.”
