SPIDERS

In California spiders are common, but most of them are not harmful to humans, and in fact are beneficial by eating insects and other garden pests. When spiders do bite humans, it is rarely dangerous; slight discomfort in the bite area is usually all that results. Spiders are probably blamed for more bites than they actually commit. Mites, bedbugs, fleas, and other insects tend to leave similar bites that might become infected.

However, some individuals may have allergic reactions to bites. If this occurs, it is helpful to be able to tell what kind of spider was responsible for the bite. If possible, capture the spider (preferably alive) and take it with you to a doctor for identificaton. Washing the bite with soap and water is advised as first aid.

There are a few relatively rare species of spiders in California whose bite can be dangerous. These include black widows and brown spiders.

Black widow venom is a very toxic nerve poison. Fortunately, the amount injected from a black widow bite is very small. Furthermore, black widow spiders are shy and generally do not like to live near humans. Doctors can treat for black widow bites, which are very rarely fatal.

The Brown Recluse Spider (Loxosceles reclusa) is not found in California. A close relative, Loxosceles deserta, the Brown Spider, is found in Southern California. Brown spiders prefer the foothills and the Sonoran and Mojave desert regions. They are an extremely shy spider and will try to avoid contact with humans, but they can become "house" spiders and are occasionally found in dry, undisturbed locations such as attics, closets, garages, and other places where goods 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. Upon biting, Brown Spiders produce a wide spectrum of reactions.

For both black widows and brown spiders, the bite is usually painless and may go unnoticed. Over the next few hours, the area becomes painful and swollen. The victim may also have nausea and malaise. In a small number of people, a brown spider bite 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. For severe cases of black widow bite, some people may experience difficulty in breathing and profuse perspiration. However, most bites of both kinds are mild and the symptoms diminish on their own over a few days.

Tarantulas are found in the warmer, drier parts of California, such as the Mojave Desert. Despite their large size, they are not considered dangerous to humans. They are capable of inflicting a painful bite, but they rarely do so, and their venom is not toxic. Regular washing with soap and water to prevent infection should be all that is necessary. Tarantulas are often safely kept as pets and can live 30 years!

Sources:
http://health.ucsd.edu/poison/spiders.htm
http://lancaster.unl.edu/enviro/pest/factsheets/006-94.htm
http://www.desertusa.com/july96/du_taran.html

Back to CEHS website:
http://www.envtox.ucdavis.edu/CEHS/Index.htm