A UC Riverside scientist is asking for the public's help to track the distribution of brown widow spiders in California. Brown widows' range expanded rapidly in Southern California since their introduction in 2003, he said, and they may move northward this summer into Central California.

"The brown widow is spreading like wildfire," said UC Riverside urban entomologist Rick Vetter. "It's a very prolific pest. People find them by the hundreds in places where they haven't seen spiders before."

Another widow species is the black widow, which is native to California. When the weather warms up, it's not uncommon to find the glossy black spiders with their tell-tale red hourglass abdomen mark in wood piles, under flower pots and in webs strung across undisturbed niches low to the ground.

Brown widow spiders are native to Africa and are established in tropical environments throughout the world. They have been found in Florida for many decades, but only recently expanded their range from Texas through South Carolina, and into southern California. As of 2009, the spider was established in Los Angeles, Orange and San Diego counties, and in 2010 it made its way to Riverside, San Bernardino, Ventura and Santa Barbara counties. There have been a few finds in areas further north.

"I've gotten three females from Sacramento and three females from Washington (state)," Vetter said. "I've gotten no other spiders from those areas, so I don't know if they will be another infestation area or not."

The brown widow poses less of a health threat than black widows, but Vetter said there are several reasons why the agricultural community should be concerned about their potential northward migration. Currently little is known about brown widow spider biological control. While black widows prefer low hangouts, it is not yet known whether brown widows will adjust to higher posts in California. If the spiders take up residence in fruit orchards, for example, they could pose a problem for farmworkers.

"Pickers and harvesters won't want to have these spiders falling down on them," Vetter said.

Brown widows could also potentially congregate in agricultural shipping containers or packaging.