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Common Spiders of California - UC Berkley
Brown Widow Info - UC Riverside
Vector-borne Diseases

Spiders

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Black Widow Spider in its Web

How To Protect Yourself From Spider Bites

Spider Facts
Spiders eat insects like flies, ants and crickets.  Many people are scared of them, but they can be helpful.  Most spiders are not a threat to humans, but some contain venom that is harmful. 

Spiders rarely bite humans, and usually do not break the skin.   Some poisonous spider bites can cause swelling, tissue damage and disturb the function between nerves and muscles that can lead to paralysis.  The only poisonous spiders in San Diego County are the  Black Widow, Brown Widow and the Desert Recluse.  Please note that we do not have the Brown Recluse in San Diego County.

Black Widow
The adult female Black Widow spider has a shiny, black, round abdomen with a red hourglass figure on the underside of it's abdomen.  Adult females are about 1/2-inch long, not including the legs.  Adult male Black Widow spiders are harmless, and about half the size of females.  The male's abdomen usually has red spots and white lines or bars.  

The Black Widow Life Cycle
Black Widow spiders mate in the spring and summer.  The female lays eggs in a silken sac that is about 1/2 inch in diameter.  Each sac is hung in the spider's web and is white at first and later turns tan or gray.  It usually contains 25 to 250 eggs. After about 4 weeks in the sac, the spiderlings hatch.  They become adults in 2 to 4 months.


Black Widow Spider and its Egg Sac

Symptoms of a Black Widow Spider Bite

The initial pain from a spider bite can cause an intense and burning sensation. Common symptoms include:

  • Sweating
  • Nausea
  • Rapid heartbeat
  • Muscle spasms
  • Blurred vision
  • Trouble breathing and swallowing
Inflamed Spider Bite

Children under the age of 6, people over the age of 60 and people at risk for cardiovascular disease are at risk of  having problems from a poisonous spider bite.  Some people may also have allergic reactions that can cause circulatory failure.   To see if they are going to have an allergic reaction, they may be kept under observation for 24 hours. 

Brown Widow
The Brown Widow was first established in San Diego and Los Angeles County in early 2000. Since then it has become a common member of the local urban spider population in San Diego County and continues to expand it's numbers across Southern California.  They are mottled tan and brown in appearance.  Like the black widow, they also have a hourglass figure on the underside of their abdomen, however it is orange in appearance rather than red.  

Brown Widow and it's Egg Sac

Desert Recluse
The Desert Recluse is not the same as the Brown Recluse.  It is found in the Sonoran and Mojave deserts, the foothills of lower Joaquin Valley and areas close to the Mexican border.  They prefer to live in remote unpopulated areas.  They are nocturnal spiders, meaning they only come out at night and they live under rocks and in old animal burrows.

How To Avoid Spider Bites

  • Wear shoes outdoors
  • Do not put your hands in holes, under furniture and in woodpiles where you cannot see them
  • Shake out clothing, towels, shoes, gloves and boots before each use
  • Use caution  when using outdoor toilets, as they are favorite places for spiders to hide

Treatment of Spider Bites

  • Wash the bite mark with soap and water to help prevent infection
  • Rub ice cubes on the bite to numb and reduce the pain
  • Seek medical attention right away for Black Widow, Brown Widow and Desert Recluse spider bites
  • For other spider bites, seek medical attention when necessary

Controlling Spiders
To keep spiders out of your home, you can take the following steps:

  • Clean up woodpiles and leaves around the home
  • Seal cracks on the house foundation, and around windows and doors
  • Use a high-pressure hose to spray spiders on outside walls
  • Make sure you are not carrying them in your home on plants and in boxes
  • Vacuum or sweep windows, corners of rooms, storage areas, garages and basements to help remove spiders and their webs

Vacuuming spiders can be an effective control technique because their soft bodies usually do not survive this process. Webs that are gathering dust are old and no longer being used by a spider.

Chemical Control
Spraying insecticide may also keep spiders under control.  Make sure that the product is right for your home and be sure to follow the label instructions carefully.                          

If you find a spider that may be dangerous and you would like to identify it, please contact the County of San Diego Vector Control Program at (858) 694-2888. 

For More Information On 
 Spiders Or Other Vectors Contact: 
(858) 694-2888  
vector@sdcounty.ca.gov
 Vector Control Program