Spiders adapt their webs to filter out human-made noise

Since the Industrial Revolution, the world has witnessed a sharp increase in noise pollution generated by human activities. Whether it’s the constant hum of traffic, airplanes overhead, or the repetitive clamor of construction, these sounds can obstruct animals’ abilities to give and receive crucial signals – a process that is fundamental to their survival and reproduction.

Now, a team of biologists at the University of Nebraska–Lincoln (UNL) has published one of the first known studies demonstrating how one group of animals can react to human-made noise by adjusting its own method of sensing sounds. 

In an article published in the journal Current Biology, researchers Brandi Pessman and Eileen Hebets show that funnel-weaving spiders alter how their silk webs transmit vibrations in response to local noise.

This finding suggests that the spiders might deliberately change web structure to cope with the auditory chaos surrounding them, ensuring they receive vital cues from potential mates, prey, or predators.

A key discovery about web adjustments

Drawing on lab experiments, the study uncovered a particularly unexpected insight: the way a spider’s web conveys vibrations varies depending on whether its architect was collected from a rural or urban area. This discrepancy hints at the idea that prior exposure to noise – possibly even inherited across generations – may influence a spider’s malleability when it comes to spinning webs.

“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 lead author of the paper.

“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.”

Spider webs as sensory extensions

It has been well documented that animals such as birds and frogs can change their calls or the timing of their vocalizations in the face of increased human noise. However, little was known about how animals manage to tweak the way they receive acoustic or vibratory signals.

The main challenge is the hidden nature of most animals’ sensory systems, which are located within their bodies. But web-building spiders are unique, as their webs function effectively like external sensory extensions that capture vibrations from the environment.

This distinction makes funnel-weaving spiders, also known as Agelenopsis pennsylvanica, an ideal test group. They rely predominantly on vibratory signals for vital information. Their webs connect to various surfaces – trees, rocks, or buildings – capable of transmitting the vibratory noise created by traffic, industrial activities, and more. 

The research team hypothesized that funnel-weaving spiders might be able to reduce the volume of unwanted or irrelevant vibrations caused by human-related noise, which often shares the frequency range these spiders need for effective communication.

Spiders in urban areas

Pessman started by collecting a total of 60 funnel-weaving spiders in and around Lincoln, Nebraska – some from city settings and others from out in the countryside. In the lab, the spiders were then placed in controlled environments that were either quiet or noisy as they spun webs over four nights.

Upon completion, the researchers introduced test vibrations into those webs, measuring how energy moved across the silk in different conditions.

They observed that spiders from urban areas tended to build webs that lost more energy in short-distance vibrations across a broader set of frequencies when placed under noisy conditions.

Interpreted practically, these webs essentially “muffled” environmental noise. This may prevent sensory overload, giving the spiders a clearer signal from prey or other relevant vibrations in their immediate vicinity.

Spiders that are exposed to less noise

Meanwhile, rural spiders assembled their webs in such a way that energy from biologically important long-distance vibrations was preserved. This indicates they might be amplifying or enhancing certain frequency ranges to pick out meaningful vibrations above the background noise.

“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.”

Implications for ecology and future studies

Given the role of funnel webs as external sensory structures, these findings open a new window into how animals can adjust the way they receive signals, a research area that had remained largely unclear until now.

The ability to alter web structure in response to different noise environments could prove vital as human-made noise continues to escalate across the planet.

In the future, the team plans to investigate precisely how the spiders are changing their webs – whether they adjust the tension of certain silk lines, vary anchor points, or adopt an entirely new shape to filter or boost specific frequencies.

High-speed video of the web-building process, combined with digital tracking methods, will let them delve deeper into these construction nuances.

Spiders overcoming environmental noise

“This study really highlights the role of receivers in overcoming environmental noise,” said Hebets, who is a professor of biological sciences at UNL.

“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?”

By revealing that some species can modify their “sensor” for hearing, the team hopes to inspire more research on how other animals cope with rising noise levels.

The funnels built by these little invertebrates may seem inconsequential to an urban passerby, but as the study shows, each strand of silk can be precisely tuned to help the spider thrive in a clamorous world.

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