Almost all spiders produce toxic venoms, but their fangs are too small and weak to penetrate the skin, the venom is too weak, the volume of venom is too small to pose a significant threat for humans. The black widow (Latrodectus mactans) is the only spider found in the United States that is capable of routinely producing serious illness by its bite. The "tarantula" native to the U.S. Southwest bites only after extreme provocation. Its weak and ineffective fangs can only penetrate thin skin, such as that on the sides of the fingers; the effects of the bite are no worse than an insect sting. In other parts of the world are spiders that can cause severe, even fatal poisoning in humans. Other species of Latrodectus produce effects similar to the black widow. The bites of large, hairy tarantulas found in areas such as Brazil or Peru can have similar results. The Sydney funnel web spider, reportedly limited in distribution to the area within 100 miles of Sydney, Australia, is capable of inflicting a bite that can be lethal for healthy young adults.
Some spiders, such as the brown, or violin, spider (Loxoseeles recluse) inflict bites that occasionally cause extensive damage at the site, but usually have less severe generalized effects. The jumping spider (Phidippus) is the most common biting spider in the United States. Bites by this spider, trapdoor spiders, orb weavers, and spiders of the Chiracanthium species, such as the garden spider, commonly produce local reactions that ulcerate and less often produce systemic symptoms. However, individuals with these bites almost never require hospitalization. Spiders usually cling to the site of the bite. (If the spider can not be found, some other arachnid, such as a bedbug, should be suspected.) Anyone who has been bitten should take the spider to be identified.
Rarely, an individual may be bitten repeatedly by a relatively harmless spider or insect and develop an allergy to the toxin produced by that species. Subsequent bites can produce severe, even fatal allergic reactions. Fortunately such events are rare. The treatment for such reactions is identical to the treatment for allergic reactions to insect stings.
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