BITE, SPIDER

Arachnids are the group of insects that include spiders. The main poisonous biting spiders in the United States are brown recluse spiders, black widow spiders, tarantulas, and hobo spiders. The bite of each produces different symptoms and requires different treatment. Brown recluse spiders are common in the southernmost states but may be found as far north as Wisconsin. The black widow is common in every state except Alaska. Tarantulas live in the South and the Southwest but are also popular pets, so they may show up anywhere. The hobo spider is found in the Pacific Northwest. Although most spider bites are uncomfortable, they are not particularly dangerous and will heal without long-term problems.

Signs and symptoms of brown recluse spider bites often include a stinging sensation at the time of the bite followed by redness and swelling. In severe bites, a blood-filled blister may form in 1 to 3 days that will then break down into an ulcer that may take 2 to 5 weeks to heal. Infection can be a problem and if the ulcer is large enough, it may require skin grafts. Symptoms of the hobo spider bite may be similar, but may also include headaches and muscle aches.

Black widow spider bites usually cause an intense burning at the time of the bite. There will not be much to see at the bite. Many times this is all that will happen. In some cases, about 30 to 60 minutes after the bite, spasms of the abdomen, limbs, and back occur. Elevated blood pressure, sweating, and vomiting may accompany the spasms. All symptoms usually resolve within a few days. Tarantula bites resemble a wasp sting with severe pain, redness, and swelling at the site of the bite that will resolve in a few days without further problems.

For brown recluse bites, start treatment with cold packs and elevation if the bite is on a limb. You should get a tetanus shot if you are due for one. If the ulcer has a lot of dead tissue in it, your doctor may cut some of it out (debride it) to allow the ulcer to heal faster. If an ulcer is large, skin grafting may be necessary. There is a medicine called dapsone that may be helpful if an ulcer is forming, to limit its size and to promote healing. Dapsone may have allergic side effects and causes anemia in some individuals. If there are signs of infection in the bite, you may need antibiotics. Treatment for hobo spider bites is similar, but dapsone may not help.

For black widow bites, ice is the first treatment. You should get a tetanus shot if needed. Pain medicines and muscle relaxants will help severe pain or muscle spasms. There is an antivenin available but only for very severe cases, such as when individuals are having trouble breathing or in pregnant women, because antivenin treatment has a high risk of causing allergic reactions. For severe bites, many patients are admitted to the hospital for 1 to 3 days. They stay until the spasms and elevated blood pressure have resolved.

For tarantula bites, elevation of the limb and oral pain medicines are usually adequate. Some tarantulas have hairs on their bodies that cause severe itching if they get into the skin; steroids and antihistamines may help with the itching. You should get a tetanus shot if needed.

• If bitten by a spider, you should rest the area bitten, keep it elevated, and consider applying ice. As outlined above, most bites will resolve on their own. You should take pain medicines and antibiotics as prescribed.

• The best way to treat spider bites is to watch out for the spiders. Most of these spiders are not aggressive, and most try to avoid human contact. The one exception is the hobo spider, which can be aggressive. Be careful when searching in little-used closets, attics, and basements. Especially for the brown recluse, you should shake out and carefully inspect stored bedding or clothes before using them if they have been in storage for any time. If you keep spiders as pets, you should know what the potential for bites is and how to treat them. Remember that many tarantula species can also cause itching if you come in contact with the hairs on their body, so avoid handling those species. The hobo spider lives outside on paths and gardens and can be aggressive if its web is disturbed. If you live in an area where it lives, you should learn to recognize its web so that you can avoid it.

• If a brown recluse bites you, call your doctor if the ulcer gets larger than about three fourths of an inch in diameter or if it looks as if the ulcer is becoming infected. It may need more treatment, such as with dapsone or an antibiotic. For black widow bites, report any new onset of painful muscle spasms, especially if you are having trouble breathing, are pregnant, or have any chronic health problems.

Paul Auerbach (ed): Wilderness medicine, ed 3, St Louis, 1995, Mosby. Hobo spiders (and a page on brown recluse spiders and one on black widow spiders)
http://www.srv.net/~dkv/hoboindx.html

Tarantulas
http://www.cowboy.net/~spider/ATS.html

All biting insects and spiders
http://entmuseum9.UCR.edu/ent133/ebeling/ebel9-1.html




Brown recluse and black widow spiders may produce extensive tissue necrosis and ulceration (From Noble J [ed]: Primary care medicine, ed 2, St Louis, 1996, Mosby.)

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