The invasive pest spotlight focuses on emerging or potential invasive pests in California. In this issue, we cover the brown widow spider.

Adult brown widow spider with egg sacs. Photo by Mike Lewis, CISR.

Brown Widow Spider Facts

The brown widow spider became established in Southern California in 2000 and appears to be displacing the black widow in some of its habitats, especially in urban areas. They build their webs in secluded areas around homes and in vegetation. Mature female brown widows are smaller than mature female western black widows. The normal brown widow spider coloration is a mottled mixture of tan, brown, and gray. It has a lengthwise stripe halfway up the back side of the abdomen with two isolated dots in front of it and diagonal stripes on the side. The brown widow spider does have an hourglass, but it is typically orange rather than the vivid red of a black widow. Male brown widows are much smaller than other widow spiders. Like black widows, brown widow spiders make irregular webs of strong silk. The egg sac of the brown widow spider has protuberances of silk all over its surface, resembling a very large pollen grain. The sac is so characteristic that it can be used to confirm that brown widows are present even if the spiders themselves are not seen.

What can you do?

The bite of the brown widow spider is much milder than the black widow so the risk of serious injury from their bite is less. If you spot a brown widow spider in your garden or around your home, manage it as you would any spider. Clear up clutter like wood piles to reduce nesting sites. Check under patio furniture for nesting spiders and sweep down their webs.

For more information on widow spiders, visit http://ipm.ucanr.edu/PMG/PESTNOTES/pn74149.html.