Wolf spider’s hunting rate may peak at 85 degrees

Hexbyte Glen Cove

Schizocosa saltatrix, a species of wolf spider native to North America. Credit: Stella Uiterwaal

Since the mid-20th century, ecologists have been studying how the availability of prey affects the rate at which predators kill and consume it. Depending on the animals and the ecosystem, predators do tend to consume more prey as more of it becomes available—but often only to a point, beyond which that consumption rate levels off.

With temperatures trending upward across much of the world, ecologists are also keen to understand how global warming might sway the predator-prey dynamics that have emerged over thousands of years. Because rising temperatures speed the metabolism that fuels movement, which in turn drives predator-prey encounters, many ecologists have predicted that prey consumption will increase more-or-less in tandem with . But some recent research suggests that the warming-hunting relationship might have its own threshold, with consumption rates instead peaking and dropping when ecosystems surpass certain temperatures.

Nebraska’s John DeLong, Stella Uiterwaal and Alondra Magallanes investigated the issue with the help of Schizocosa saltatrix, a species of wolf , and the tiny flies, or midges, commonly eaten by those spiders.

The trio began by collecting 60 wolf spiders and roughly 620 midges from Cedar Point Biological Station, a Husker research site near Ogallala. The team placed each spider inside a petri dish containing between three and 20 midges. Each sat atop a heating pad set to one of four settings: (72 to 78 degrees Fahrenheit), low (80 to 85 degrees), medium (86 to 90 degrees) or high (91 to 97 degrees). After 30 minutes, the team counted the number of midges killed and eaten by each spider.

Rather than escalating indefinitely, the wolf spiders’ consumption of midges peaked at about 85 degrees Fahrenheit—roughly the highest conceivable temperature that the nocturnal species would be accustomed to hunting in. If that phenomenon holds across other predatory species, could potentially increase foraging among nocturnal while curbing it among species that hunt by day, the researchers said.

The current study is published in Climate Change Ecology. More could help pinpoint which of the many potential causes are responsible for the threshold found in the study, the team said. Understanding how fast consumption does increase alongside warming, and the temperatures at which it peaks in various species, should also allow researchers to better predict the ecological outcomes of climate change.

More information:
John P. DeLong et al, Temperature has a unimodal effect on the functional response of wolf spiders, Climate Change Ecology (2022). DOI: 10.1016/j.ecochg.2022.100063

Wolf spider’s hunting rate may peak at 85 degrees (2022, October 13)
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Hexbyte Glen Cove Huge spiders to colonize US East Coast, but maybe it’s a good thing

Hexbyte Glen Cove

This undated image courtesy of Ben Frick from the University of Georgia shows a Joro spider (Trichonephila clavata).

Big and scary-looking Joro spiders have spread from Asia to the southern United States and are now poised to colonize the country’s cooler climes—but they’re nothing to fear and might end up actually helping local ecosystems.

That’s according to scientists who have been studying the arachnid invaders since they first arrived in Georgia around 2013.

In a few short years, the golden webs spun by the bright yellow, dark blue and red spiders have become a common sight throughout the state, and new research suggests they will clamber up the Eastern Seaboard next.

“The reason we got involved in this project was because they literally fell in our lap,” Andy Davis, an ecologist at the University of Georgia, told AFP on Friday.

“They’re kind of everywhere here in North Georgia, they’re all over my backyard.”

Davis set about studying the new resident, comparing it to the golden silk spider, which came to the southeastern United States some 160 years ago from the tropics.

Writing in a paper published in the journal Physiological Entomology, he and his co-author Ben Frick found similarities but also striking differences between the relatives.

The Joro spider’s metabolic rate is about double that of its cousin, its heart beats 77 percent faster, and it can survive brief freezes. They also grow faster.

Together, these traits mean it can better survive colder climates, which is not completely surprising, given that it is native to temperate Japan.

They’re also adept at gliding—spinning webs that act like parachutes and catch air currents—allowing them to fly up to 100 miles (160 kilometers).

The paper examined records from iNaturalist, which tracks sightings of animals, and found that the spider’s range had already spread far beyond Georgia to encompass the nearby states of South Carolina, North Carolina and Tennessee.

In a few short years, the Joro spider’s golden webs—which they tend to build at head height—have become a common sight throughout the US state of Georgia, and new research suggests they will clamber up the Eastern Seaboard next.

There was even a report from faraway Oklahoma.

Left to themselves, Joros would probably work their way up the coast over 20 years, but it’ll probably happen faster if they hitchhike on vehicles, said Davis.

Call for clemency

That’s likely how they arrived in the United States in the first place—either a female stowaway laid her eggs when she landed on a ship, or an egg sac was brought over and hatched in spring.

Invasive species are often linked to destruction—such as the spotted lanternfly, a native of Southeast Asia that came to the US state of Pennsylvania in 2014 and is known to decimate and .

But the Joros’ exploding numbers aren’t necessarily a cause for concern, argued Davis.

“The golden silk is everywhere in the southeast, and it’s not causing any harm. It’s been here so long, it’s integrated itself into the ecosystem, and the Joro could follow the same trajectory,” he said.

In fact, it could provide a hearty meal for native predators, such as mud dauber wasps, which hunt spiders. Other beneficiaries could include local lizards.

Another advantage: Joros also feed on insects that local spiders do not, such as the adult brown marmorated stink bug.

They’re also not aggressive towards humans, nor are their fangs big enough to pose any kind of threat, stressed Davis, who called for clemency and understanding, not stigmatization.

“I don’t really think the Joros deserve to be squashed or killed like the spotted lanternfly—they’re really not out to get us and it’s not their fault either that they’re here. They were literally along for the ride,” he said.

© 2022 AFP

Huge spiders to colonize US East Coast, but maybe it’s a good thing (2022, March 11)
retrieved 12 March 2022
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