Brown widow egg sacs look something like giant pollen balls.

“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.”'

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.

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.”

Vetter is asking the public to assist in his brown widow spider research by carefully following instructions for collecting and sending brown widow spider specimens to the university. Potential spider collectors should study the photos on his website to learn the characteristics of brown widows. Because the spider is already established in Southern California, Vetter does not need specimens from San Diego, Orange, Los Angeles and the Riverside and San Bernardino-Redlands area. More specimens are welcome from Ventura, Santa Barbara, from Riverside and San Bernardino counties outside of the urban cities in the western part of the counties and from all the rest of California.

For spider shipping instructions, see Vetter’s brown widow spider research page.

Watch an 80-second video for tips on identifying brown widow spiders: