Drop for drop, brown widow spider venom is more toxic than the venom of their black cousins, but other characteristics make them less dangerous, according to Vetter. Brown widows are less likely to bite. Instead, they curl up, drop and play dead when disturbed. They do not defend their egg sacs. When brown widows do bite, they release less venom than black widows.

However, brown widows will have the advantage of numbers. Black widows are known for their anti-social tendencies, usually occupying space alone. Brown widows have no such fondness for solitude.

"Where you might find six or seven black widows in a backyard, now you find 100 brown widows," Vetter said.

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 at http://cisr.ucr.edu/brown_widow_spider.html 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.

Immature black widow spiders are often confused for brown widows because they look alike: mottled tan, brown and gray body with an orange or yellow hourglass on the abdomen. Vetter said the easiest way to distinguish the spiders is their egg sacs. Black widows' egg sacs are smooth, teardrop shaped and a little yellowish; the brown widows' egg sac has spiky protrusions that make it look like a large pollen ball.

"People have sent in a lot of different things already thinking they are brown widow spiders and they've been wrong," Vetter said.

Spiders may be shipped dead or alive. Good quality digital images may also be submitted. For submission instructions and the mail and email address, see Vetter's brown widow spider research page at http://cisr.ucr.edu/brown_widow_research.html.