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The Informed Parent

Spider Bites

by Louis P. Theriot, M.D., F.A.A.P.
Published on Sep. 06, 1999
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As four year old Michael lifted up the sleeve of his T-shirt revealing a silver dollar sized, red, tense, raised area with a smaller 1 centimeter crusted lesion in the center, his mom anxiously asked, "Well, what do you think...black widow or brown recluse?" She went on to explain that this has been a particularly bad summer for spiders at their house. She herself, had killed no less than five black widows around the garage, and she said that these spiders were hardly shy and hidden in dark corners. They had spun their webs in highly visible areas. She had the exterminator to her house twice to spray.

I gathered more history and learned that Michael’s bite had been there for around three days and it didn’t bother him other than the fact that it itched. He was otherwise perfectly fine. She pressed on further, "Well, which is it? My husband and I have a bet and he says it’s a brown recluse". She had a perplexed look on her face when I replied, "Neither!" It was not the response she was expecting, and it took all of the suspense out of the moment.

I then went on to explain to her about spider bites. Virtually all spiders have venom and teeth, and that is how they protect and defend themselves. In Southern California however, the two main groups of spiders that have jaws capable of penetrating the human skin to deliver the venom and be of medical importance are the black widow and brown recluse. They cause very different problems.

The black widow is found throughout the United States except in the extreme north. There are five species of Latrodectism and only three of these are actually black. Only one species, L. mactans, has the characteristic hourglass figure on the underbelly and this can be red, orange or even yellow. They prefer warm, dark dry places such as the basement or garage. The venom of the black widow lacks agents that are locally toxic to the tissue. Therefore, there is no tissue damage at the sight of the bite. In fact, the bite often goes unnoticed, or the victim may report a fleeting pin-prick sensation and nothing more. Within the hour, there may then be an achy, uncomfortable sensation is the area where the bite occurred, and this may involve an entire limb. The lymph nodes in the area become tender and very painful. This is followed by a target or halo lesion that appears around the bite and is characteristic of a black widow evenomation. This halo or target fades in a few hours and is easily missed. The victim then goes on to develop more systemic symptoms which include muscle spasms, cramping, pain in the chest or back, nausea, vomiting, sweating, a fast heart rate and high blood pressure. The sweating pattern may uniquely involve the upper lip or tip of the nose. These symptoms may last for 36-72 hours.

People in the extremes of life, young infants and the elderly, are more at risk to have serious and dangerous reactions especially hypertension. For the most part, the treatment of a black widow bite involves pain control, close monitoring of the blood pressure, relief of the cramping, and insuring good hydration. There is a black widow anti-venom available that is made from horse serum, but this is reserved for life-threatening evenomations because it is not without risk.

The brown recluse or violin/fiddleback spider belongs to the genus Loxosceles of which there are twelve species. They have a characteristic violin marking on their head and thorax. The most commonly found spider of this genus found in the United States is the L. reclusa, or brown recluse. They are especially common the the south. The brown recluse is a nocturnal hunter and prefers dark, undisturbed areas like woodpiles, basements or under rocks. It, too, is unaggressive and shy except when trapped or attacked.

The venom of the brown recluse does contain "cytotoxins" or agents that are destructive to human tissue and cause tissue necrosis. The bite is almost painless and usually goes unnoticed. Within 1-2 hours of the bite, there is burning and itchiness at the sight followed by redness, swelling and severe pain. Over a couple of days, this progresses to form a bluish-gray blister that sloughs leaving a necrotic ulcer that may be as large as 7 inches in diameter. There may also be systemic symptoms such as fever, chills, nausea, vomiting and joint aches. A number of different modalities have been tries to halt or prevent the tissue damage but none has proven to be optimal. These include antibiotics, steroids, surgical excision, hyperbaric oxygen and high dose electrical current. The entire lesion will resolve with time, but this may take up to weeks or months and may leave disfiguring scars.

In managing both black widow and brown recluse bites, proper care should be taken to clean and dress the wounds, and it is important to be sure that tetanus prophylaxis is up to date.

Michael’s mom could easily see why his bite could not have been from one of these spiders. It was frustrating to think that his bite was most likely from an insect of a sort, the exact one would never be known. It could have been from one of hundreds of type of insects. At least he would be fine...and at least her husband didn’t win the bet.




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