Spiders of Medical Importance
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: 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. Should a 
Black Widow Spider bite occur, contact the Regional Poison Center for advice. Not all patients need emergency 
room treatment, since in some cases the spider injects no venom. We can help you decide what treatment is 
required. Other than washing the wound with soap and water, there is no effective first-aid treatment.

 << Black Widow  ||  Diagram >> 
 << Bite Marks  ||  Bad bite >>  

Brown Spiders: The Brown Recluse Spider (Loxosceles reclusa) is not found in California. A close relative 
Loxosceles deserta is found in Southern California except along the coast. Brown spiders have never been found 
in San Diego County west of the mountains as they prefer the foothills and the Sonoran and Mojave desert 
regions. They are an extremely shy spider and will try to avoid contact with humans. They are nocturnal hunters 
and their primary habitat is outdoors where they are found in brush piles, beneath stones or boards or other 
objects on the ground. They can become "house" spiders and are found in dry, undisturbed locations such as 
attics, closets, garages and other goods that are stored for prolonged periods of time. An additional species, 
Loxosceles laeta, was imported into Los Angeles County from South America, sometime prior to 1969. It has 
become well established in Sierra Madre, Alhambra, El Monte, San Gabriel, Monterey Park and Highland Park and
is likely to be in other adjacent cities as well.

 << Recluse  ||  Range >> 
 << Bite Marks  ||  Bad bite >>  

Upon biting, Brown Spiders produce a wide spectrum of reactions. The bite is usually painless and may go 
unnoticed. Over the next 8 hours, the area becomes painful and a blue-gray area of discoloration resembling a 
"bulls-eye" surrounds the bite site. In most patients, nothing more develops and the area heals. Some victims 
develop a blister at the bite site that becomes a slow healing ulcer about 1 centimeter in size. They may also have 
nausea and malaise. In a small number of people, the ulcer extends to greater than 4 centimeters in size, may 
become infected and is accompanied by fever, destruction of red blood cells and possibly kidney failure. Surgical 
repair of the wound may be required. Most bites are mild and fit into the first two groups. The third type of reaction 
is rare in this area of the state. There is some indication that the Loxosceles laeta species may produce more 
severe reactions than Loxosceles deserta.
It is important to remember that not all skin lesions that occur are caused by spider bites and in particular by 
Loxosceles spiders. Many spiders are capable of producing mild skin lesions when they bite. If these do not 
become infected, they usually heal in a short period of time. Many other biting insects, such as fleas, ticks, 
bedbugs, assassin beetles and others can cause wounds that initially resemble brown spider bites. Most "Brown 
Recluse Spider Bites" usually turn out to be infected wounds caused by one of these other types of biting insects. 
Documented encounters with Loxosceles spiders in Southern California are very rare. Brown spider bites do not 
produce wounds except at the site of the bite. Recent newspaper accounts, that attributed reactions in patients 
that required multiple limb amputations to brown spider bites, were more likely from the increasingly described, 
highly virulent Streptococcal infections that produce gangrenous limbs requiring surgical amputation.

Please Read The Website Disclaimer!
Copyright 1986-2012, The Survival & Self-Reliance Studies Institute (SSRsi), All Rights Reserved
Site conceptualized, designed, created & maintained by MEG Raven
Snail Mail: SSRsi, PO Box 2572 Dillon, CO. 80435-2572