Brown widow spiders are beginning to displace the more dangerous black widows in some parts of California, according to a story in the Riverside Press-Enterprise.

The brown widow spider, a native of South Africa, made its first American home in Florida. It became established in Southern California in the early 2000s and its range continues to expand. As of 2009, the spider was known in Los Angeles, Orange and San Diego counties, but as of 2010, it has shown up in Santa Barbara and Sacramento counties.

"They're very prolific," said Rick Vetter, a UC Riverside urban entomologist who is documenting the species' spread in California. "Where you might find six or seven black widows in a backyard, now you find 100 brown widows."

The mottled tan, brown and gray spiders - like their black cousins - carry the signature hourglass marking on the abdomen, however the brown widow's mark is orange or yellow instead of red. They can also be distinguished by their egg sacs; the brown widow's has spiky protrusions.

Vetter told Press-Enterprise reporter Janet Zimmerman there is concern the brown widow will make its way to California's Central Valley, where they could have an impact on the agricultural industry.

"People don't want the spiders shipped around on their produce," Vetter said.

Although brown widows may congregate in greater numbers and their venom is more potent, the spiders pose less risk than black widows. Brown widows are less likely to bite. Instead they curl up when disturbed and do not defend their egg sacs. When they do bite, they release less venom than black widows.

"Most of the bites recorded so far have been very mild," such as pain and redness at the bite site, Vetter was quoted in the story.

Vetter asks that California residents outside of LA, Orange and Ventura counties send him samples of brown widows they find so he can track their spread. For more information, see Vetter's webpage.