This spider web is strong enough for a bird to sit on, a scientific first

This spider web is strong enough for a bird to sit on, a scientific first

Published November 14, 2022

6 min read

On September 13, 2022, Atlanta-based naturalist and garden expert Arty Schronce looked out his kitchen window and saw what he thought was a female cardinal trapped in a huge, golden spiderweb. That would have been a strange sight, but Schronce discovered that the bird was not stuck. It was actually perched on a web and taking swipes at the large, yellow and red arachnid who made it: a Trichonephilaclavata invasive joro spider.

After the spider was scared off, the cardinal gobbled up a few of the insects that had become caught in the web. It flew off.

The entire encounter lasted only two minutes, but Schronce knew he had just witnessed something extraordinary. The spider was still there when Schronce checked again the next day. The web was unharmed.

“This is incredibly unusual,” says Andy Davis, an expert on joro spiders at the University of Georgia.

Birds stealing food out of spiderwebs is a documented behavior–but in previous instances, the birds were recorded as doing so while hovering or perched on a nearby branch, Davis and Schronce report today in a study published by the journal Insects. There are also reports of birds getting trapped in spiderwebs or collecting spider webs for their nests. However, nobody has ever reported a bird sitting on a spider web.

” This is a scientific first, Davis says. Schronce said that the experience has made it clear to him how important citizen scientists are: “We can all learn and observe, and maybe even see something that has never before been recorded,” he said. Schronce, a long-time photographer, wishes he had a better camera.

Webs of a different color

The brightly colored joro is thought to have been accidentally introduced to the United States in 2014 via a shipping container from East Asia, where the species is native. Although they are harmless to humans, the red, yellow, and black arachnids can grow up to as large as an adult’s hand.

(Read about how scientists believe the joro spider could spread throughout the eastern United States. )

What’s more, the joro comes from a genus of orb-weavers well known for spinning large, tough webs. The golden silk spider, another species from this genus, has also been introduced into the United States. It is named for its yellow-ish silk.

Coincidentally, only a few months before Schronce observed the bird perched in the joro web, Davis had performed a series of tests to determine the spiderwebs’ strength as part of an elementary school science fair project with his son, Oscar.

The father-and-son duo used a fine thread to loop an electronic force gauge over the top of 10 joro webs of similar size. The duo pulled the webs down gently until they gave way. They recorded the Newtons force (a unit of measurement that measures the force required to accelerate one kilogram of mass at a rate of one meter per hour every second).

The measurements the Davises took found that the joro webs could hold an object weighing up to 2.4 ounces (69 grams). This means that one could easily support a cardinal, which is a bird that weighs in the neighborhood of 1. 48 and 1. 72 ounces (42 and 49 grams).

(Learn why scientists say spider silk is one of the most versatile materials on Earth. )

“Four or five months later, this guy calls me and says he’s found a bird sitting on a web,” Davis recalls. “And then I kind of put two and two together and realized that I had data that basically showed the same thing.”

Oscar won the science fair–and Davis gained valuable support for the new finding.

‘A pretty bizarre thing for a cardinal to do’

Cardinal expert Daniel Baldassarre says he’s never seen one of these common North American birds do anything like this. Baldassarre, an ornithologist at State University of New York Oswego, says that cardinals are not small birds.

They aren’t a bird that forages in such delicate ways. Cardinals spend a lot time hunting for food on ground and are less likely to do the “tightrope walking”, which Baldassarre claims is more common among birds that forage in the forest canopy.

“They’re just kind of more awkward and kind of lumbering in the way they forage,” he says.

Cardinals are also known for their exploratory behavior. He says that cardinals have an aspect of their biology that allows them to eat almost anything.

It’s not surprising that the bird took a few insects from the web, a behavior called kleptoparasitism.

” But it’s still quite a bizarre thing for a bird to do,” Baldassarre said.

While so far the behavior has only been documented once, Davis wonders if more native birds might start to catch on to the potential benefits presented by these new, large spiders and their webs. The dewdrop spider, a native kleptoparasite, seems to be making the most of this situation.

“These little spiders kind of make their living hanging out on other spider’s webs and stealing their food,” says Davis. “In all the joro webs I’ve seen this fall, I’ve probably seen these dewdropspiders on at least 30 percent of them. So the dewdrops are benefiting big time from the joros.”

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