A Brown Widow spider, displaying the famous red hourglass marking under her abdomen, guards her egg sacs near Archer, Fla., Sept. 3, 2004.
A Brown Widow spider, displaying the famous red hourglass marking under her abdomen, guards her egg sacs near Archer, Fla., Sept. 3, 2004. (AP Photo/Phil Sandlin)

They're messy, poisonous and prolific.

But at least they keep out their cousins, who are even worse.

Families venturing out this spring can now see the unique egg sacs of the brown widow spider, an invasive arachnid that is increasingly displacing black widow spiders in California's backyards. The egg sac is round and distinctively spiky, like a white cotton naval mine.

Brown widow spiders love to place their egg sacs on the bottom side of chairs.

"They love cheap, plastic patio furniture," said Mark Hoddle, the director of the UC Riverside Center for Invasive Species Research.

Brown widows are close cousins to black widows. They are usually brown with white stripes, and they often have the distinctive hourglass marking common to black widows, sometimes in a more muted tone than the bright-red/orange found on black widows. They also make similarly messy, sticky webs, Hoddle said. And they wouldn't carry the "widow" name if they didn't enjoy eating a mate from time to time.

Brown widow bites are infrequent, and they aren't nearly as damaging as a black widow bite, Hoddle said.

Brown widow poison is very strong, maybe stronger than black widow poison, according to one study. Scientists are still figuring out why the bites don't do much damage.

A typical bite leaves a small red mark, according to experts. And they generally won't bite unless they are directly threatened, such as getting sat on or grabbed.

Black widow bites, while rarely fatal, tend to pack more of a punch, causing body aches and muscle soreness.

No one is exactly sure from which continent brown widow spiders hail, possibly South America or Africa.

But they're definitely not from California.

They showed up in the Golden State about a decade ago, and they started laying eggs at a breakneck pace - far faster than black widows.

These days, scientists looking in backyards find far more brown widows than black widows.

"We think they are just out breeding black widows," Hoddle said.

Now that they're here, they'll likely stay forever, Hoddle said.. Like crows and cockroaches, they do well around humans.

"They're very hardy and they're not so picky about where they live," said Stephen Goldberg, a biology professor at Whittier College.

Those with sympathy for the devil should have no fear.

Black widows will survive. They still love living in the woods or in bushes.

"They'll just be pushed out to natural areas," Hoddle said.