Brown Recluse Spiders May Invade Northern U.S. as Planet Warms

Climate change may give America’s venomous brown recluse spiders a choice: Move to a more northern state or face dramatic losses in range and possible extinction, a new theoretical study suggests.

Currently, brown recluse spiders are found in the interior of roughly the southeastern quarter of the continental United States. Researcher Erin Saupe used two ecological computer models to predict the extent of the spider’s range in 2020, 2050 and 2080 given the effects of global warming.

“The actual amount of suitable habitat of the brown recluse doesn’t change dramatically in the future time slices, but what is changing is where that area is located,” said Saupe, who was pursuing a master’s degree at the University of Kansas when she did the work. She is now a doctoral student there.

  If the projections are correct, by 2080, perhaps only 5 percent of the spider’s current range — which extends from Kansas across to Kentucky and from Texas across to Georgia, including the states in between  — would remain suitable for it. However, climate change could make portions of Wisconsin, Michigan, Indiana, Ohio, Pennsylvania, New York, Nebraska and South Dakota habitable to the spiders.

Arachnophobia

This may come as a surprise to some residents of these states. In many minds, brown recluse spiders – with their outsized reputation for bringing death, amputations and paralysis – already occupy most of the country, Rick Vetter, a research associate at the University of California, Riverside contends.

Vetter, one of the study authors, created the Brown Recluse Challenge, a 4½-year project. “I got tired of people telling me that brown recluses are all over the U.S and Canada, and I said, ‘Send them to me and I will identify them,’” Vetter said.

One thousand, seven hundred and seventy three spiders later, it was clear that any brown, eight-legged insect was at risk of misidentification as a brown recluse – 79 percent of the specimens he received from people across the country were not of the species Loxosceles reclusa, Vetter told LiveScience. 

“People fear the unknown. … They like to tell scary stories, they are willing to believe bad things about things they don’t like anyway, so there is a lot of human psychology that is wrapped around the brown recluse,” he said. [Top 10 Phobias]

The challenge has since been picked up by the University of Florida.

In nature, brown recluses live underneath bark or logs in dry areas or underneath hanging rocks. But humans also create a good habitat for them in cellars, attics and garages, according to Vetter.

Their venom contains a toxin that causes skin to die, resulting in what are known as necrotic lesions. In about 90 percent of cases, the bite of a brown recluse has virtually no effect. The other 10 percent cause severe symptoms with potentially life-threatening complications. There are no solid statistics available, but Vetter estimates that one or two bite-induced deaths occur each year, typically in small children.

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