Climate change has apparently helped a species of voracious spiders migrate from coastal South Carolina into the state’s interior.
Golden silk orb weavers, large spiders that spin webs several feet across, are among a number of exotic species are now documented as living South Carolina’s only national park, Congaree National Park.
The bodies of females can be more than 1.5 inches long, with the legs more than twice that length. Their bite has been likened to that of a bee sting, but they are not venomous.
It’s not clear how climate change has affected all nonnative species in the park, but the presence of orb weavers appears tied to rising Earth temperatures, Congaree officials say.
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“As far as species moving into the park, the golden silk orb weaver is our poster child for that phenomenon,’’ said David Shelley, the park’s education coordinator.
Winter temperatures – particularly overnight lows – were in the past too chilly for orb weavers to survive in the interior of many Southern states, scientists say. Since 1991, average temperatures have risen at Congaree National Park by at least one-half degree, according to the Park Service.
Golden silk orb weavers began showing up in 2008 at Congaree and now likely are producing thousands of eggs each year.
“Today, they are very abundant,’’ the Park Service reports in a brochure on climate change realities at Congaree.
The emergence of orb weavers at Congaree National Park is part of a regional phenomenon over the past 16 years. The spiders are being spotted in many areas well away from the coast, including central Georgia and Alabama, according to research by Kristin Bakkegard, a Samford University scientist who studies the spiders’ movement
National Park Service officials say they haven’t noticed any problems the big spiders are causing – orb weavers are relatively harmless to people – but they say more research is needed to gain a clearer picture of how the spiders might affect other animals.
When nonnative animals move into new territories, they sometimes gobble up food that native animals rely on. Or, in the case of plants, they spread rapidly and grow in soil favored by native plants, out-competing the locals and killing them off.
“This expansion complicates predator-prey relationships in unexpected ways that can ripple through the food web,’’ the park’s climate change brochure says of golden silk orb weavers.
Golden silk orb weavers were documented in South Carolina near Charleston in 1863, the earliest known occurrence of the species in the United States, according to Bakkegard’s research. They are found widely in the tropics and may have reached Charleston and other destinations by ship.
Orb weavers aren’t as venomous as other spiders and their bites would be less painful to people than a bee sting, according to researchers at the University of Florida and the website venomousspiders.net. The spiders will bite only if held or pinched, say Florida scientists.
Orb weavers can be different colors, but many are gold or orange with striped, feathery, tufted legs. Other than tarantulas, female orb weavers are among the largest spiders in North America, according to the University of Florida.
In the orb weaver’s world, females are so large and dominant that they are threats to eat male orb weavers as the smaller spiders try to mate with them. Some scientific research indicates that the quarter-inch males try to mate with female orb weavers while the larger spiders are distracted and dining on other bugs, such as flies, wasps or bees.
“Males presumably wait until the female is eating in order to avoid cannibalism,” according to a 2011 research paper about the mortality risks in spider mating, which was published by the Oxford University Press.
This year, orb weaver webs were easy to spot along the boardwalk at Congaree National Park near the visitor’s center.
Spider webs stretched several feet across. The colorful spiders sat motionless in the middle of the webs, waiting to ensnare an insect before attacking.
Some park visitors weren’t sure they liked the sight of a big spider hanging from a web as they walked the boardwalk. Others delighted in seeing orb weavers because they were so colorful.
For now, golden silk orb weavers have disappeared for the winter after laying eggs that will pop out next spring. By next fall, the spider babies will have grown into adults and spun more big webs. Park officials say the return of the spiders will be a treat.
“Spiders have some negative cultural associations,’’ Shelley said. “They do scare some people. But these are very charismatic spiders. They are beautiful.’’
Golden silk orb weavers
They are moving from the coast to the interior of South Carolina and to Congaree National Park as the earth’s climate warms.
Golden silk orb weavers spin large golden webs to catch prey
Females are brightly colored, grow to more than 1.5 inches in body size and have legs twice as long as their bodies.
Males are duller in color and much smaller.
Males sometimes sneak up on females to mate while the bigger spiders are eating.
An orb weaver bite is considered less painful than a bee sting.
They first were documented at Congaree National Park in 2008, but have been moving inland since about 2000.
The best time to see them is in late summer and fall at Congaree National Park.
The first orb weavers documented in the U.S. were in the Charleston area during the Civil War.
Sources: Samford University, University of Florida, U.S. National Park Service, Oxford University Press, Florida State University