In laboratory experiments, spiders changed the way they built their webs in noisy environments, with rural and urban spiders responding differently to sounds.
Life in the city can be noisy. Natives get used to the cacophony, but the rumble of traffic, sirens, air conditioners and the hustle and bustle of people at all hours of the day and night can be disconcerting to a newcomer. A new study shows that some spiders have similar experiences.
Researchers compared spiders from rural and urban environments and found that they change the way they build their webs when exposed to noise, but their coping strategy depends on what kind of sound exposure they have experienced in the past, according to a paper published this month in the journal Current Biology.
"urban and rural spiders respond differently when placed in noisy environments," said Brandi Pessman, a biologist at the University of Nebraska-Lincoln and lead author of the study. "This means that spiders with different experiences with noise - whether they have experienced it themselves or their relatives have passed it down to them from generation to generation - respond to it differently."
The team's focus was the Pennsylvania grass spider (Agelenopsis pennsylvanica) from the Raven family widely distributed throughout North America. These creatures build conical, tube-shaped webs that are not sticky. They wait until unsuspecting prey is caught in the funnel and then move quickly to bite and immobilize their food.
This technique depends on the spider being able to instantly recognize the vibration when the insect bumps into its web. Any extraneous noise could make this difficult. "They really rely on these precise vibrations to determine where prey is, what kind of prey it is, and whether it's worth attacking," Pessman says.
The researchers collected spiders from urban and rural areas and then brought them to the laboratory. There, they placed the spiders in containers equipped with speakers that played loud or quiet sounds for four days. At the end of the experiment, they analyzed the webs by applying vibrations to them and monitoring the spider silk's response.
In the face of loud sound, spiders from urban areas wove webs that dampened the vibrations, while rural spiders, on the contrary, amplified it.
Essentially, urban spiders responded to noise by soundproofing it - their webs sort of muffled the sounds of the environment. In general, such webs transmitted fewer vibrations to the spider. This adaptation may also block out sounds made by potential mates or certain prey species, but it also allows urban spiders to pick up nearby prey without feeling uncomfortable.
At the same time, the rural spiders, unaccustomed to loud noises, reacted by making their webs more sensitive to try to detect prey amidst the constant noise. For rural spiders, it was like turning up the volume to better hear the radio while the blender was running.
"Celestial spiders are not used to so much noise in their environment," Pessman says in his study. "When they are suddenly bombarded with a lot of noise, they may try to 'turn up' the volume in their web or amplify incoming signals to better hear certain cues over the noise."
The researchers still aren't sure exactly how the spiders make these changes to their web, and plan to explore the mechanisms in future studies using video and tracking programs. For now, they hypothesize that it may have to do with the placement of anchor points, silk tension, or the overall structure of the web.
This isn't the first time scientists have investigated spiders' response to noise or tested the sensitivity of their webs to vibrations. In 2017, a study found that populations of spiders and other insects decline near noisy gas compressors, and last year scientists turned to studying the structure of the web to try to create a more sensitive microphone.
Beth Mortimer, a biologist at Oxford University in England who was not involved in the new study, said that "the feeling of vibration tends to be the most neglected sense in the natural world."