Since the Industrial Revolution, human activity has led to a surge in environmental noise. The sounds of traffic, airplanes, construction and more clutter the outdoor soundscape, challenging animals’ abilities to send and receive information — which is critical to their survival and reproduction.
A University of Nebraska–Lincoln biology duo has published one of the first studies demonstrating that one type of animal, when faced with human-generated noise, is able to alter how it receives sound-based information. In a recent Current Biology publication, Husker biologists Brandi Pessman and Eileen Hebets demonstrated that the webs of funnel-weaving spiders transmit vibrations differently in response to increased local environmental noise. This flexibility in web transmission properties suggests that the spiders may intentionally spin their webs differently to manage surrounding noise and receive crucial sensory information.
In a particularly novel finding, the study also shows that individual webs transmit vibrations differently depending on whether the web’s architect was collected from an urban or rural environment. This suggests that a spider’s past exposure to environmental noise — and possibly its genetic makeup — shapes its web-building flexibility.
“One of the most interesting things that we found is that urban and rural spiders are reacting differently when they’re put into a noisy environment,” said Pessman, a postdoctoral researcher in biological sciences and the study’s lead author. “This means that spiders with different experiences with noise — whether they themselves experienced it or their mothers passed it down to them across generations — respond differently.”
The study marks a major advance in understanding animals’ management of environmental noise. It is well established that certain species alter their communication production as a workaround: Some birds delay their dawn chorus until aircraft noise diminishes, and brown tree frogs increase the pitch of their songs to avoid overlap with traffic noise frequencies, for example.
But to this point, little has been known about how animals change their reception of sound. This gap is due, in part, to the difficulty in studying animals’ internal sensory structures, like the networks of nerves that enable hearing. But spiders are unique in having an external sensory structure: their webs, which they use to elicit clues about predators, prey, potential mates and their overall environment. Because of this, the spider and its web serve as a unique gateway for gleaning information about sound reception amid noise.
Pessman and Hebets’ study focuses on vibratory noise, the dominant form of communication for funnel-weaving spiders, also known as grass spiders or, formally, Agelenopsis pennsylvanica. Their webs frequently connect to surfaces like trees, rocks and buildings, which are conduits for vibrations caused by environmental noise like traffic and machinery. The researchers hypothesized that grass spiders may use their webs to guard against these human-made vibrations, which often overlap the frequency range that spiders use for communication.
To test this theory, Pessman collected a total of 60 funnel-weaving spiders from both urban and rural areas in and around Lincoln, then exposed them to either quiet or loud vibratory noise as they spun webs over four nights. Then, the researchers applied different vibratory stimuli to assess how sound traveled across the webs.
For the spiders from urban areas who built webs under loud noise conditions, the team found that the webs lost more energy in short-distance vibrations across a broader frequency range than any of the other groups. In other words, these spiders — who are accustomed to constant, high-amplitude noise — built webs that essentially quieted their environment. This is likely a means for avoiding excessive stimulation, protecting their hearing ability and enabling them to more precisely detect nearby prey.
Another key finding arose from the rural spiders who spun webs amid loud noise. Pessman and Hebets found that these webs retained energy in biologically relevant, longer-range vibrations. This means these spiders tuned their webs to enhance incoming vibrations at a particular frequency — likely to help them home in on important environmental cues.
“Rural spiders are not used to as much noise in their environment,” Pessman said. “When they suddenly get a lot of noise, they might try to ‘turn up’ the volume in their webs or amplify what’s coming in to better hear certain signals above the noise.”
That the spiders were able to fine-tune their webs to adjust sound reception in a certain frequency range — possibly without affecting the web’s function at other frequencies — reflects a sophisticated means of coping with environmental noise and paves the way for research on parallel strategies in other animals.
“This study really highlights the role of receivers in overcoming environmental noise,” said Hebets, George Holmes Professor of biological sciences. “It opens up entirely new avenues of research. For example, are receivers placing themselves at certain locations in the environment where signals are going to receive less attenuation or overlap of noise? Even without being able to go into the nervous system, other people can start looking at ways that receivers might be adjusting to increase the relevant signal-to-noise ratio.”
Pessman said the next step is determining how, exactly, the spiders are changing their webs’ sound transmission properties — whether it is modifying their structure, the tension of the silk, the location or number of anchor points, or something else entirely. They plan to explore these questions using video of the spiders building their webs, as well as tracking software that allows the researchers to reconstruct the webs.
Funding from the National Science Foundation Graduate Research Fellowship Program supported this work.
