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Brown widow spiders "taking over" in Southern California

July 02, 2012|By Eryn Brown, Los Angeles Times / for the Science Now blog
  • A brown widow spider collected in Irvine. The species is a relatively recent arrival to Southern California.
A brown widow spider collected in Irvine. The species is a relatively recent… (Mark Boster / Los Angeles…)

As far as anyone knows for certain, brown widow spiders have only resided in Southern California for a decade or so -- the first in the region was spotted in Torrance in 2003. But a new survey conducted by California entomologists shows that the spider is now making itself quite comfortable in our neck of the woods. 

In some Southern California habitats, including the outdoor areas around suburban houses, the brown widow far outnumbers its cousin the black widow — a California native long feared for its venomous bite.

“The brown widow is really taking over,” said Richard Vetter, a staff research associate at UC Riverside and coauthor of a paper detailing the survey, being  published Monday in the Journal of Medical Entomology. Collecting data at 72 sites in Orange and Riverside counties, Vetter and his colleagues found brown widows at a rate 20 times greater than the rate at which they found black widows — at least, when they searched around people’s homes. 

That’s because unlike black widows, who like to crawl into cracks and under debris for shelter, brown widows like to hide out in people’s things. They gravitate toward the crannies underneath chairs and into those downward-facing recessed handles on garbage cans.

“Cheap patio furniture is great stuff. They love it,” said Vetter, who has upturned a single molded plastic chair and seen five to eight brown widows hanging out in the niches underneath. “They like a solid top,” he added. “If you have a mesh top, or fabric mesh, I don’t know if it’s the air or the light, but they don’t like that.”

The entomologists also frequently found brown widows under the supports on wooden fences, in the nooks beneath plastic playground equipment and in “the curled lips of potted plants.” They did not find brown widows in houses, and only rarely found them in garages, sheds, wilderness or agricultural areas. 

The researchers counted black widows, too, and found them in larger numbers in agricultural areas and in xeric (drought-friendly) landscaping.

The brown widow’s apparent success in Southern California doesn’t mean it has pushed aside the black widow. Vetter said it was not uncommon for an invasive species to find a new habitat, spread like gangbusters at first, and then see its population dwindle a bit as it reaches a new equilibrium. That has been the recent experience in Georgia, he said.

The main thing Homo sapiens will want to know about Latrodectus geometricus? Although it’s venomous, its bite isn’t as dangerous as that of the black widow.   

It hurts initially, and then there’s some burning at the site, but that’s usually all, Vetter said.

“Mostly, nothing happens,” he said.

Click here to visit Vetter’s webpage and learn more about brown widow spiders.


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