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Black widow populations drop as spider falls prey to brown widows

Black widow populations are declining in parts of the southern United States as the spider becomes prey for the non-native brown widow, according to new research. Photo courtesy of National History Museum of Utah
Black widow populations are declining in parts of the southern United States as the spider becomes prey for the non-native brown widow, according to new research. Photo courtesy of National History Museum of Utah

March 14 (UPI) -- Black widow spiders could face extinction in parts of the southern United States, as they become prey for the non-native brown widow, according to new research.

The research, published Monday in the Annals of the Entomological Society of America, found that black widows are slowly being displaced by invading brown widows in a pattern first discovered a decade ago.

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While there are three native species of black widow spiders in the United States, brown widows are believed to be native to Africa, according to researchers who say brown widows are now seen on all continents except Antarctica.

Since its introduction into Florida, the non-native brown widow has displaced the state's southern black widow and has quickly expanded into urban areas as far north as Kansas and as far west as California.

While black widows are known for their poisonous bite, they are not aggressive if unprovoked. In comparison, brown widows grow faster and are twice as fertile, producing more egg sacs than southern black widows.

Brown widows are also six times more likely to kill and consume "shy" southern black widows, according to researchers, than other cobweb spiders.

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As the study ruled out competition for scarce prey or disease as the reason behind the decline in black widow spider populations, the study is the first to blame aggressive predation by brown widows.

Researchers found that brown widow spiders killed and ate black widows in 80% of their confrontations. While some of the encounters ended with the two spiders cohabiting, none ended with the black widows showing aggression.

"Brown widows are not labeled invasive. They're still non-native," said study lead author Louis Coticchio, a spider biologist specializing in the widow and recluse families, in an interview with Gizmodo. "If it does come out that the introduction of brown widows is absolutely the main reason why we're seeing a huge decline in black widow populations, I would love to see the attitude towards them changed."

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