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Brown Widow Spiders Becoming More Prevalent In California

July 3, 2012
Image Caption: The ventral (under) side of a brown widow spider, Latrodectus geometricus with the orange hourglass marking clearly visible. Captured and photographed in Los Angeles, California. Credit: Matthew Field/Wikipedia

redOrbit Staff & Wire Reports – Your Universe Online

First discovered in Florida in 1935, Brown widow spiders are still considerably new to North America. However, after being discovered in southern California in 2003, they have been so successful that they may be displacing native black widow spiders.

Researchers believe that the overall hazard to homeowners may decrease because brown widow spider bites are less toxic than those of native western black widow spiders.

In the Journal of Medical Entomology study, titled “The Prevalence of Brown Widow and Black Widow Spiders (Araneae: Theridiidae) in Urban Southern California,” the authors describe the results of their efforts to document the presence of brown widows in southern California. They conducted timed searches in various habitats, such as urban properties, agricultural lands, parks, and not fully formed natural areas. They also included the native western black widow spider to compare the abundance and habitat selection of the two species.

“The brown widows really burst on to the scene in a very short time, and we found brown widows in many habitats where we expected to find black widows,” said corresponding author Richard Vetter from the University of California, Riverside.

“There may be some competition where brown widows are displacing black widows because there is some habitat overlap. There are also places where only brown widows were able to make homes, but in other habitats the black widows still predominate.”

After collecting data at 72 sites, which involved over 96 hours of collecting, the authors found 20 times as many brown widows than black widows outside homes, especially under outdoor tables and chairs, and in tiny spaces in walls, fences and other objects. Neither spider is found inside living space of houses.

“Homeowners would benefit to know about the hiding places of brown widows, displaying care when placing their hands in nooks and crannies,” the authors conclude. However, they should also keep in mind that even if the chances of being bitten do increase, the dangers are lessened because the brown widow bite is less toxic than the black widow.


Source: redOrbit Staff & Wire Reports - Your Universe Online



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