Why these gigantic spiders love to be near traffic

With incessant din of road noise and vibration from heavy traffic below, a perch atop a highway streetlight would seem an unpleasant abode. Yet that’s one unusual environment where joro spiders, invasive in the United States since 2014, and their kin often spin their webs. Now researchers have taken the pulse of these arachnids to get a better sense of how they live in such noisy locales.

Female joro spiders make large shimmering webs, often clustered in trees like an arachnid apartment complex. But their webs also show up on gas pumps, in busy parking lots and near multi-lane thoroughfares where tens of thousands of vehicles pass daily.

Previous research on these spiders has shown them to be shy creatures that startle easily. And yet, “they seem to be able to tolerate these crazy, very disturbed environments,” says Andy Davis, an animal ecologist at the University of Georgia in Athens. The finding, recently published in the journal Physiological Entomology, showcases a new method to study insect stress and hints at why joros have adapted to city life so well.

(Female invasive joro spiders may dabble in cannibalism.)

Webs in the city

Davis and Erin Grabarczyk, a behavioral ecologist at Valdosta State University in Georgia, wondered if the spiders, with their penchant for human-dominated locations, even experienced stress from road noise. So they and their students collected joro spiders (Trichonephila clavata) and golden silk spiders (Trichonephila clavipes), a joro cousin that also builds its webs in surprising spots, from loud and quiet locales in Georgia. Many of the golden silk spiders were captured from trees along a six-lane highway, Grabarczyk says. Meanwhile, the quiet environments had almost no daytime traffic.

Back at the lab, the team placed the spiders in enclosures and waited until they had built webs or strung up some support lines. Then with speakers next to the enclosure, they blared pink noise that mimicked the roar of traffic and recorded the subtle rise and fall of the spiders’ abdomens caused by their beating hearts with high-magnification cameras.

Stress in a heartbeat

Spiders’ hearts are shaped like tubes through which blood flows, and their walls squish in and out rhythmically as they beat. “Surprisingly,” Davis says, “the typical heart rate of a spider isn’t that far off from humans’.” Human heart rates are typically between 60 and 100 beats per minute while these spiders’ rhythms are usually 50 to 100 beats per minute, he says.

Like humans, when spiders experience stress, their hearts sometimes race. “It’s really just a convenient way to measure stress because you can see it,” he says. Back in 2024, Davis and his colleagues first measured heartbeats in these species and two others while the arachnids were at rest and while they were under duress.

Based on their web-slinging tendencies, the scientists thought that perhaps the creatures wouldn’t show a stress response to traffic noise. “So seeing their heart rates actually rise was a surprise,” Davis says. But the reactions were muted in comparison with the heart rate responses recorded for stressed spiders in the earlier study.

With noise, “yes, they’re getting stressed, but it was overall a pretty mild stress response,” Grabarczyk says. Their noise tolerance might help explain why these arachnids have been able to spread so quickly, including in urban areas.

Good and bad vibrations

Watching heartbeats is a “really unique and clever and a non-invasive way of getting at that information,” says Eileen Hebets, an arachnologist at the University of Nebraska-Lincoln who wasn’t involved with the study.

The two species responded somewhat differently. Joros from loud environments had the highest bump in how much their hearts thumped after noise exposure. For golden silk spiders, prior noise exposure seemed to matter less. Those whose hearts beat faster at rest responded most to the loud noise. Hebets wondered whether differences in these species’ lifecycles and individual variation, such as spider pregnancies, might help explain these trends. Still, the results provide some much-needed data on how these arachnids interact with their environment and whether they have advantages that allow them to succeed where other species don’t.

There’s “surprisingly little” that people know about how environmental noise impacts animals that get information from vibrations, Hebets says. Spiders can receive vibrations from their web or whatever they’re sitting on as well as sound through the air. “So they’re actually getting double the noise,” she says.

Hebets’s group recently showed that webs made by spiders collected from noisy environments and quiet environments had different acoustic properties including how they dampened noise. “It seems like spiders are actually able to adjust their webs in some way to accommodate noise,” Hebets says. “And we know almost nothing about that.” It’s possible that joro and golden silk spiders may be able to use a similar strategy to help them tolerate noise.

(Are “giant, flying” joro spiders really taking over the U.S.?)

Roadside oasis or stress fest?

Even though joro spiders are invasive in the U.S., the study could inform insect conservation efforts because it spotlights how transformed environments like roads impact spiders. Some of the ways that spiders and other animals sense the world, such as through vibration, are ones that humans pay little attention to, Hebets says. 

Plenty of previous research has shown that living near roads stresses animals. “But I think this is one of the first studies that shows that same pattern in an arthropod,” Davis says. A similar study could have been done with grasshoppers or ladybugs, he says.

Planting roadsides as pollinator habitats can seem like a clear conservation win, Davis says. “But people forget that it’s really noisy, and it’s really stressful. And that stress can have long-term implications for critters.”