LYCOS RETRIEVER 
Spiders: Species
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Spiders are a large (more than 38,000 described species worldwide), distinct, and widespread group. The earliest evidence of spiders comes from a 380 million year old (Devonian) fossil. Spiders occur in many types of habitats and are often very abundant. Typical temperate habitats may support up to 800 individual spiders per square meter. Point estimates of spider diversity suggest that more than 600 species may be found in a single hectare of tropical forest.
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Spiders are the largest group of arachnids. There are more than 35,000 species throughout the world that are named including 3,000 in North America. There are hundreds more that have not yet been identified. They are all predators and live on plants, in trees, under rocks, on the ground and water.
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Spiders are generally carnivorous and feed only on living prey. They can crush it with processes on the pedipalps, and the chelicerae almost always have glands that can inject a venom. The bite of some large spiders can be painful, but most species are too small to break human skin, and only a few are dangerous to humans. The latter are mainly the black widow spider and its close relatives, which are nonaggressive and bite humans only in defense. Their painful bite is followed by faintness, difficulty in breathing, and other symptoms; although the bite is seldom fatal, especially if it is inflicted on healthy adults, medical attention for it should be sought at once.
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In Europe, members of the genus Tegenaria are often called house spiders since they are common inhabitants of houses and adjacent vegetation. Only a single species of Tegenaria, T. chiricahuae, is native to the United States. It occurs in caves and other dark places in Arizona and New Mexico. The other six species of Tegenaria found in the United States are of European origin. They were probably introduced to this country very early through commerce. Three species occur in the Pacific Northwest.
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Spiders are the largest group of arachnids. There are more than 35,000 named species worldwide, including about 3,000 in North America, but probably most spider species are still awaiting identification. When someone brings a spider to us for identification, it is usually large (which makes one believe it might be a Tarantula) or is marked with brilliant colors (which many believe might be a black widow), but most spiders that we are asked to identify are harmless.
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Species of Hololena and several other funnel-web spiders are common house invaders in eastern Washington (Fig. 11). Adults are commonly found in bathtubs and sinks throughout the fall and winter. These are nonaggressive spiders that pose no threat to humans. However, they could be confused with the aggressive house spider so note the abdominal markings carefully. This species lacks the chevron pattern found on the aggressive house spider.
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