Brown Recluse Spider

Spider Bites

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Recluse spiders, in the genus Loxosceles, are relatively small brown spiders with long slender legs and a distinctive darker brown, violin-shaped mark on the back of the cephalothorax (first body segment). Depending on the species, this mark may be quite obvious or subtle. Brown recluse spiders also have 3 pairs of eyes (arranged in 3 groups of two) rather than 4 pairs for most other spiders.

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Brown recluse spiders on glueboard from Oklahoma.

Recluse spiders occur throughout the southern United States, as far south as Chile. The Brown Recluse spider, Loxosceles reclusa, does not occur in the established populations of Northern California nor within approximately 1,000 miles of California, although imported individuals rarely have been collected in Riverside County. In the past 30 years there have been only four instances of L. reclusa being imported into central California in cargo crates and boxes. All of these were found in warehouses or commercial storage in low elevation communities in the Central Valley, and none have become established.

There are several related species of Recluse spiders that may occur in or near California. L. arizonica, is distributed in various parts of Arizona and may occur as far west as the Arizona-California border. Loxosceles deserta, the desert recluse, occurs in extreme southern California, and L. laeta, a tropical species, was recently introduced and is established in a very restricted area of San Diego County.

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Recluse spiders, as their name implies, are very shy and are found in sheltered locations, generally beneath objects that are rarely moved. In warmer climates they also occur under rocks or fallen wood. Recluse spiders make an irregular sheet of sticky silk beneath objects. Eggs are placed in a loose sac on the web. Encountering a recluse spider in the home is very unlikely, and is even less so in bedding or clothing. These are not aggressive spiders, and they will bite only under extreme provocation. The bite of a brown recluse spider frequently causes an initial sharp stinging sensation that quickly goes away. A small white blister usually rises at the bite site, surrounded by a large congested and swollen area. On very rare occasions, within 24 to 36 hours a systemic reaction may occur causing the victim to experience areas restlessness, fever, chills, nausea, weakness and joint pain. Typically, the symptoms are localized at the site of the wound itself, but the reaction can be severe. This is because the spider's venom contains an enzyme that destroys cell membranes causing the tissue to gradually slough away, exposing underlying tissues. Thus, the bite begins with a red zone and progresses to a gradually enlarging open sore. The sore will continue to grow and deepen to perhaps the full, thickness of the skin over a period of days or weeks, and may achieve the diameter of a dime or nickel. The sore may take as long as 3 to 4 months to completely heal. Although various medical treatments have been used or suggested, none has been demonstrated to be effective in cases of true recluse spider bites.

Brown Recluse spiders are among the most maligned of all spiders. The popular press and other sources often report highly sensational "Brown Recluse Bites". The misdiagnosis of a wound as a brown recluse bite can prevent the victim from receiving proper medical attention for the true cause of the wound. Thus, it is very important that a non-healing sore be tested to see if is caused by a bacterial infection and not erroneously diagnosed as a brown recluse bite. Some staph infections can become life threatening. For more information on these spiders go to http://spiders.ucr.edu/brs.html.

If you believe that you have found a specimen of a brown recluse spider in California, please contact the Bohart Museum of Entomology (bmuseum@ucdavis.edu) or call them at (530)752-5373. It is important for scientists to continue documenting the presence or absence of this spider in California.