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Spiders have an ominous but often undeserved reputation. In fact, they are actually helpful in controlling other pests in the home or garden since they feed on insects and other spiders. The venom of most species is not very toxic to humans, usually resulting in no more than a slight swelling, inflammation or itching sensation. Although most spiders are venomous and considered predators, of the thousands of species found in North America, few are actually considered a health threat. The two spiders that can be a health risk, however, are the black widow and brown recluse.

House Spider

House spiders are urban pests common throughout the world. They are brown in color with a body about 3/8 of an inch long. Its abdomen is spherically shaped and is colored white to brown with several dark markings. The males are typically smaller than the females and have orange colored legs; the female's legs are yellow. This spider is the most common type of comb-footed spider, named so after the comb-like row of bristles located on the tarsi of their fourth pair of legs. They tend to spin webs most often in corners, basements, crawlspaces, around windows and under furniture. Their venom is necrotic- causing open, localized wounds that may be slow to heal. Despite its aggressive nature though, reported bites from this spider are relatively rare.

Black Widow

The female black widow spider is a poisonous spider that has a somewhat round, shiny black abdomen with red markings that resembles an hourglass on the underside. The size of the body is approximately 1/2 of an inch wide and 1 1/2 to 1 3/8 inches long. They generally live under rocks and fallen trees outside the home. Inside the home, they are often found in firewood piles, basements and crawlspaces. There are five different species of the black widow spider that are prevalent in North America and despite popular opinion, the female rarely kills the male after mating.

The black widow’s venom is a neurotoxin that attacks the nervous system and may cause pain and serious illness in humans. Though the bite is not often felt, pain will develop immediately. Reactions to the black widow’s venom include increased body temperature and blood pressure, profuse sweating, dizziness, blurred vision, nausea and pain and swelling around the bite. Antitoxin is available to combat the neurotoxin. If bitten, call a physician or go to an emergency room immediately. Bites are rarely fatal when treated promptly, however, small children are at greater risk.

Brown Recluse

The brown recluse spider receives its name because of its color and isolated behavior. It is a poisonous spider that is light brown in color and about 1/2 of an inch in length. It has a violin-shaped marking on the thorax (mid-section) and is sometimes called a fiddleback spider due to this unique marking. While most spiders have 8 eyes, the brown recluse only has 6. These spiders are active throughout the year, but often go unnoticed because of their withdrawn habits. Adults can be found in dark and secluded indoor places that are dry, cluttered, undisturbed and contain a food supply of insects. There are seven species of brown recluse spider that are a health concern in the United States.

The brown recluse's venom is a cytotoxin that attacks the cells of flesh and produces necrosis, or dead tissue, in humans. Though fatalities from the venom are very rare, the reaction to the venom depends on the amount of an individual's sensitivity to the toxin. The bite is not usually felt, but a stinging sensation may develop, followed by intense pain. This reaction, however, may not occur until an hour or more after the bite. The bitten area will first develop a small, white blister and enlarge to the size of a silver dollar as the venom attacks and kills the tissue in the affected area. If bitten, call a physician or go to the emergency room immediately. Although no antitoxin is available, prompt medical treatment can prevent severe reaction and minimize the extent of damaged tissue and eventual scarring.

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