All spiders are venomous, but only two are of medical importance in Southern California.
These are the Black Widow and the Brown Spider . Black Widow Spiders are extremely common in Southern California. Fortunately, they are very shy and tend to build their webs in locations where they will not be disturbed. Encounters with humans are infrequent, with 50 to 75 bites occurring each year in San Diego and Imperial Counties. Those at greatest risk from these bites are children or the elderly, particularly those with high blood pressure or heart disease.