A few months ago, we posted a video on the blog of the most humongous disgusting spider we'd ever seen inside a house that was not a pet. A few weeks after that, we found ANOTHER one! I was getting scared that we were being invaded by something like the huge killer spider in the movie Arachnophobia. 

Then, I got really freaked out when people said that the spider we found was a brown recluse! Well, as usual, Mark did some research on the subject. It turns out that the California Academy of Sciences in San Francisco has actually been doing research on spiders in the Bay Area for years, and welcome pictures or actual (dead or alive) specimen for their research. He found what he thought was our spider (Zoropsis Spinimana, which is NOT a brown recluse and is actually harmless), and then sent some pictures to the Cal Academy for confirmation. Here was their response:

Dear Mark,

Thank you very much for your participation in the Bay Area’s Most Wanted Spider project. The photo you sent confirms that you have found a Zoropsis spinimana. Can you let me know the address where you found the spider, so we can add your sighting to our database?

The Zoropsis is native to the Mediterranean and recently became established in the San Francisco Bay Area. The first California reports of Zoropsis spinimana were found in the Sunnyvale area in Santa Clara County in 1992. Since then the spider has mostly spread north and east around the San Francisco Bay area with specimens found throughout Santa Clara, San Mateo and Alameda Counties.

Despite the fact that this spider is large enough to be intimidating, Zoropsis spinimana is harmless. It is a hunting spider (like wolf spiders), meaning it does not spin a web or use silk to subdue prey. Its silk is used primarily by the female to cover her egg sac. Like other spiders, its diet is primarily insects. Little information is available about the biology of this spider.

Most specimens that have been submitted for identification are mature males and females; this means that people are finding wandering spiders that are searching for mates, roaming in search of food or for other reasons. Mature spiders have been found from September to May and are commonly encountered throughout the winter. It is not known where the immature spiders spend the summers or if this spider requires more than one season to mature.

Thank you and we hope you will participate on the project again!

Thanks,
Alison

Alison Young
Citizen Science Educator
California Academy of Sciences
55 Music Concourse Dr.
San Francisco, CA 94118

www.calacademy.org