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Desert Gardener: Spider awareness

August 25, 2001|By ERIC T. NATWICK, University of California-Imperial County Cooperative Extension

Most people dislike spiders. The mere mention of spiders can strike fear in the heart of some people.

Spiders are beneficial to man because they prey on insect pests and other arthropod pests and few species harm people. Most spiders have toxic venom, which they use to kill their prey. However, only those spiders whose venom causes a serious reaction in humans are called "poisonous" spiders. Spiders commonly seen out in the open during the day are unlikely to bite people.

Spiders do not seek out people to bite them. Generally, a spider doesn't try to bite a person unless it has been squeezed, laid upon or similarly provoked to defend itself. The jaws of most spiders are so small that the fangs cannot penetrate the skin of an adult person. When a spider is disturbed in its web, it may bite instinctively because it mistakenly senses that an insect has been caught. If bitten by a spider, remain calm and promptly seek medical advice; it is helpful if the offending spider can be caught and saved for identification.


Spider bite first aid treatment should follow these steps, 1) wash the bite, 2) apply an antiseptic to prevent infection, and 3) use ice or ice water to reduce swelling and discomfort. If the bite causes an unusual or severe reaction, contact a physician. If you can catch the spider, preserve it for identification and take it to your county UC Cooperative Extension office.

The most common harmful spider in the Imperial Valley is the black widow spider. Black widows and their webs are usually found outdoors in dark, dry, sheltered, relatively undisturbed places such as among piles of wood, rubbish or stones; in culverts, utility meter boxes, hollow stumps and old animal burrows; and sometimes among plants. Indoors, black widows may be in garages, sheds, barns, crawl spaces and outhouses. People are most likely to be bitten when they disturb the spider while they are cleaning or picking up items in such places. A sensible precaution is to always wear gloves and a long-sleeved shirt when working in areas that have been undisturbed for a time and where there are good hiding places for spiders.

Venom from a black widow spider bite can cause reactions ranging from mild to painful and serious, but death is unlikely and many symptoms can be alleviated if medical treatment is obtained. Anyone bitten by this spider should remain calm and promptly seek medical attention.

Black widow bite symptoms range from mild to severe and are largely internal, but some local redness and swelling may develop at the bite site. Pain spreads from the bite to other parts of the body, muscular spasms may develop and the abdominal muscles may become rigid. Other effects can include profuse sweating, fever, increased blood pressure, difficulty breathing and speaking, restlessness and nausea. Typically, the pain and other symptoms reach a maximum within a day of the bite, then gradually subside over the next two or three days. Most people who are bitten spend a few hours under observation by a physician but do not develop symptoms severe enough to require treatment. Small children, the elderly and persons with health problems are likely to suffer some of the more severe consequences of the bite.

Spiders are primarily beneficial and their activities should be encouraged in the garden. Pesticide control is difficult and rarely necessary. The best approach to controlling spiders in and around the home is to remove hiding spots for reclusive spiders such as black widows and regularly clean webs off the house with brushes and vacuums.

Spiders enter houses through cracks and other openings or they may be carried in on items like plants, firewood and boxes. Vacuuming is a good way to remove individual spiders. Sweep or vacuuming windows, corners of rooms and storage regular to remove spiders and their webs. Seal cracks in the foundation and gaps around windows and doors to prevent spiders from coming indoors. Screening of attic vents windows and doors will keep out many spiders and will discourage them by keeping out insects, their prey.

In indoor storage areas, place boxes off the floor and away from walls to reduce habitat favored by spiders. Tape boxes or use self-sealing storage containers to prevent spiders from taking up residence. Regularly clean storage areas in garages, sheds and basements, but wear gloves to avoid accidental bites.

Outdoors, remove webs and spiders from buildings regularly by using a broom, mop, garden hose or vacuum. Eliminate places for spiders' habitat by keeping the area next to buildings free of trash, leaf litter, heavy vegetation and other accumulations of materials. Trim plant growth away from the house and other structures to discourage spiders from taking up residence.

Insecticides do not provide long-term control and should only be used selectively against spiders outdoors. Regular nighttime searches with a flash light will help find black widow spiders along building foundations. The spiders can be killed with a broom, with a rolled up newspaper or your shoe or a vacuum. Aerosol insecticides can be used to kill black widow spiders but the spray must directly contact the spider as spray residues do not have a long-lasting effect.

Insecticide control is only temporary and must be accompanied by housekeeping. There are various insecticides available in retail outlets labeled for spider control, including pyrethrins, resmethrin, allethrin or combinations of these products.

Questions? Send mail to: Desert Gardener in care of Cooperative Extension, 1050 E. Holton Road, Holtville, CA 92250 or send e-mail to:

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