The next time you sweep away a cobweb without a second thought, consider this: the silken structure is an engineering marvel. According to new research published last week in Current Biology, a North American spider species can change how its webs transmit vibrations.
The authors have reported that spiders in urban environments can build webs that filter out loud ambient vibrations. Conversely, spiders from quieter rural spaces build webs that amplify biologically relevant vibrations they need to pick up in their noisy environment.
Webs in folklore and science
Spiders and their remarkable weaving abilities have been celebrated in folklore for thousands of years. West African folklore tales of Ananse, the trickster spider that could turn human, celebrate him as a wise creator. In Greek mythology, Arachne was a skilful woman who defeated Athena in a contest by weaving a flawless tapestry. She was turned into a spider in her afterlife, and goes on to create beautiful webs, or so the tale tells us.
Webs are tools of creation in mythology as well as material science. Spider silk is known to be an amazing natural material with unique properties. It has inspired researchers to develop materials derived from spider silk with applications in tissue engineering and regenerative medicine. They are also studying the unique combination of strength and flexibility in spider silk for use in textile production.
A few decades ago, researchers began to study how vibrations in webs transmit critical information for spiders.
For the first time, however, researchers from the University of Nebraska-Lincoln, Brandi Pessman and Eileen Hebets, have shown that spiders can alter how they receive vibratory information in loud environments.
Vibratory information from the web is crucial for spiders because they don’t have ears. Pessman, the lead author of the study, said, “Webs are more than just nets that catch bugs. They’re actually extensions of the spider’s sensory system.”
Spider ‘hearing’ in a noisy world
The researchers studied one species of funnel-weaving spiders, Agelenopsis pennsylvanica, a species spread all over North America. They weave a funnel-shaped web into which they retreat to protect themselves from predators. Unlike their cousins that build orb-shaped webs, these spiders don’t build sticky webs. Instead, this species uses just real-time vibrations in the web to sense when there’s prey in it, then jumps out and injects them with venom.
Pessman noticed how sensitive these spiders were to vibrations. “Even my footsteps disturb the spiders, so they’d run into the retreat and hide,” she said. She then started exploring how the spiders used the vibrations to detect prey. Pessman would tape a toothpick onto a vibrating toothbrush, then place the toothpick onto the funnel web. “The spider would reliably come out and attack the toothpick because they think it’s prey,” she recalled.
The researchers collected spiders both from a noisy city and its peaceful country surroundings and brought them back to the lab. They built small arenas for the spiders with a speaker at the bottom that played loud or quiet white noise to both urban and rural spiders.
Over the next four days, the spiders built their webs in these conditions. After this, the researchers tested 60 webs by sending controlled vibrations through them at either short or long range (3.5 cm and 7 cm, respectively, from the opening of the retreat), and recorded energy transmission. What they found was very illuminating.
“It’s like the spiders are using their webs as their own personal volume dial,” Pessman said.
When confronted with loud noise, city spiders built webs that dampened energy from a broad range of frequencies (300-1,000 Hz) at the short range. On the other hand, rural spiders built webs that retained energy in a narrow range (350-600 Hz) from the long range.
What this means for urban wildlife
The difference between city and rural spiders only emerged when the spiders were blasted with loud white noise, suggesting that spiders built their webs differently to manage ambient noise. However, it is very difficult to prove whether they do so consciously.
That said, the new study naturally raised questions about what its findings mean for the animal communities living in rapidly urbanising spaces around the world. “We need a lot more studies across animals before we can really begin to generalise,” Pessman said. “Cities are a very difficult place for animals to live and there are not many animals that have accomplished such a feat of being able to do so well in cities.”
Shannon Olsson, a researcher in urban ecology, chemical ecology, and sustainability, said, “This [study] suggests that chronic exposure to urban environments impacts the way spiders build their webs and respond to environmental cues.”
Olsson, who wasn’t involved in the study, also pointed out that whether these changes are indeed an adaptation to urban noise and whether these changes actually affect prey capture remain to be tested. As she summed it up: “Regardless, that urbanisation impacts how spiders construct their home and source of food is an important result.”
Similar needs for spiders, humans
India’s urban centres are notorious for their noise pollution. While the government has defined upper limits to curb noise pollution, cities regularly make the news for exceeding them. “Noise pollution is a huge issue in Indian cities,” Olsson said. “Generally, people compensate with soundproof walls and sound barriers. However, increasingly, researchers are showing the impacts of noise on our wildlife and calling for action.”
How much of a concern is noise pollution compared to, say, carbon pollution?
“Globally, we have what is known as ‘carbon tunnel vision’,” Olsson, who is also the founder and global director of the ‘echo network’, an international programme connecting 2,500 members across 46 countries that works on global sustainability challenges. “Yet other stressors such as air, light, and noise pollution arguably have greater immediate impacts on the plants and animals we rely on for survival.”
In India and worldwide, there is a growing need to study and communicate the diverse consequences of human beings on wildlife. In the mythology of the Cherokee, an indigenous North American people, the spider web is a metaphor for the connections among all living beings, highlighting all of nature as a deeply interconnected community.
As Olsson added, “These funnel web spiders are important pest controllers for a habitat, but they need lots of food to eat, and clean and safe places to build their homes. Their needs are not too different from us, in the end.”
Vrinda Ravi Kumar is an evolutionary biologist based in the Czech Republic.
Published – April 29, 2025 05:30 am IST