Environment & Science

Riverside professor studies spread of brown widow spider

The brown widow spider, Latrodectus geometricus, is believed to be from Africa or South America. Researchers say it is expanding across California.
The brown widow spider, Latrodectus geometricus, is believed to be from Africa or South America. Researchers say it is expanding across California.
via UC Riverside's website

Listen to story

Download this story 0.0MB

A UC Riverside entomologist is studying the spread of the new kid on the web in Southern California: the brown widow. That poisonous spider didn’t appear in Southern California until about eight years ago, but it’s spread quickly since then.

The Inland Empire reported its first brown widow sightings two years ago.

"This thing has spread quickly," says UC Riverside spider expert Rick Vetter. "It was not in Riverside or San Bernardino in 2009. Last year, it was all over the place. And it’s now starting to show up in Ventura and Santa Barbara County. And (we) have no idea if it’s going to stop there or if it’s going to be plentiful this year."

So far nobody has found the spider in eastern Riverside and San Bernardino counties or north of Santa Barbara.

Vetter is tracking the spider as people send him brown widow samples from areas where the non-native spider is not yet known to be established.

"It seems to be the consensus that black widows are being pushed out by the brown widows," Vetter says. "The thing is, the brown widow is found in a lot of places you would never find a black widow. Like, they’ll be underneath a wrought iron railing or underneath those solar powered lights that you stick in the ground on your walkway. You would never find a black widow in that much of an exposed area."

Vetter says a bigger span of territory means more brown widows.

"It just goes from people having five or six black widows to having 50 to 100 brown widows. And that’s something that you typically would not ignore," Vetter says. "I mean, the black widows, you can say, 'OK, I’ve got a few black widows. It’s fine.' But if you look at the brown widows, they’re just everywhere."

Brown widows can sometimes be hard to distinguish from immature black widows. The brown widows are the same shape as black widows, but are a mottled color. Both have a red hourglass shape on their undersides.

Vetter says the egg sac is the dead giveaway. He says black widows have round, smooth yellow egg sacs.

"The brown widow has an egg sac that looks like a pollen ball. It has all these little spikes on it," he says. "And it looks like one of those World War II harbor mines that were floating around in the harbor, blowing up ships."

Brown widows carry the same sort of venom as black widows do, but they’re not as aggressive. They’ll even pretend to play dead rather than bite. And their bites are not only rarer, but tend to be less severe than black widow bites.

Still, Vetter says they’re so new to the area, we don’t know much about them, such as what pesticides will kill them and whether they will move into agricultural areas, which could pose a risk for farm workers.

Vetter would like to get some answers with his research.