DATE: 9/12/07

CONTACT:  Ian Stocks, (864) 656-5058, ians@clemson.edu

WRITER:      Diane Palmer, (864) 656-4741; spalmer@clemson.edu

Is it really a brown recluse?

CLEMSON – The brown recluse spider may be getting more credit than deserved for putting the bite on residents of South Carolina.

The number of skin lesions diagnosed as brown recluse bites by physicians in South Carolina is far greater than the number of brown recluse spiders that have been collected, according to a study published in the Journal of the American Board of Family Medicine. 

The study was done by Dr. Ivar Frithsen of the Medical University of South Carolina, Richard Vetter of the University of California at Riverside, and Ian Stocks, Clemson University researcher with the Department of Entomology, Soils and Plant Sciences.

The three conducted the research to evaluate the evidence for brown recluse spiders in the state. The spider bite diagnosis data was collected from 1990 and 2004 surveys of South Carolina physicians. 

South Carolina doctors diagnosed 478 brown recluse spider bites in 1990 and 738 in 2004.  Since 1953 only 44 brown recluse specimens have been verified from six locations in Pickens, Greenville, Abbeville, Chester, Lexington and Charleston counties.

This could be in part because of the limited number of spiders that were collected and brought to the physicians, according the study. Misdiagnosis may also be part of the disparity.

The spiders have been collected exclusively from man-made structures, leading the scientists to conclude that these spider populations are localized and unlikely to spread through natural habitats.

Alternate causes of skin lesions that have been mistaken for the brown recluse include methicillin-resistant Staphylococcus aureus (MRSA), an emerging infectious disease in many parts of the United States, according to the study.  The severe pain experienced by patients with MRSA skin infections is likely the reason they think they have been bitten by a spider. 

The study also emphasizes that numerous other medical conditions can result in symptoms that are often diagnosed as brown recluse bites, and a diagnosis of brown recluse bite may mean that the real condition goes untreated.

The brown recluse belongs to a group of spiders that seek and prefer seclusion.  The risk of being bitten by a brown recluse is so low that occupants of homes with hundreds of spiders may never be bitten.

Brown recluse spiders often have a dark violin marking on the back, with the neck of the violin pointing toward the abdomen. The abdomen can range from light tan to dark brown and is covered with numerous fine hairs that provide a velvety appearance. The long, thin, brown legs also are covered with fine hairs. Adults have a leg span about the size of a quarter. Most spiders have eight eyes, but recluse spiders have six.

Several species of spiders found in South Carolina resemble brown recluse spiders, making it difficult for a non expert to identify the spider correctly.

The physical reaction to a brown recluse spider bite depends on the amount of venom injected and an individual’s sensitivity.  Some people are unaffected, while others experience immediate or delayed effects as the venom kills tissues at the site of the bite. 

There currently are no medications or procedures that reverse the effect of the venom or speed healing, but most bite victims heal without scarring, according to Stocks. In most bite cases, current medical opinion is to let the wound heal without intervention.

Fatalities are extremely rare, although bites are most dangerous to young children, the elderly and those in poor physical condition.

“It is difficult for a physician to diagnose a brown recluse bite based simply on an examination of the wound, “said Stocks.   “It is necessary to have the spider for positive identification and not rule out other potential medical conditions too early.”

For more information about the study, contact Stocks at (864) 656-5058 or ians@clemson.edu.

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