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The phylum Arthropoda includes arachnids and insects. Although their bites typically cause only local reactions, some species are venomous or transmit
disease. The two medically important spiders in the United States are widow spiders (Latrodectus), the bite of which causes intense muscle spasms, and the brown recluse (Loxosceles), which may cause skin necrosis. Widow bites usually respond to narcotics, benzodiazepines, or, when necessary, antivenom. Most recluse bites resolve uneventfully without aggressive therapy and require only wound care and minor debridement. Tick bites can transmit diseases only after prolonged attachment to the host. Treatment of clothing with permethrin and proper tick removal greatly reduce the risk of infection. Ticks of medical importance in the United States include the black-legged tick, the Lone Star tick, and the American dog tick. The prophylactic use of a single dose of doxycycline for
Lyme disease may be justified in high-risk areas of the country when an attached, engorged black-legged tick is removed. Bites from fleas, bedbugs, biting flies, and mosquitoes present as nonspecific pruritic pink papules, but the history and location of the bite can assist with diagnosis. Flea bites are usually on ankles, whereas mosquito bites are on exposed skin, and chigger bites tend to be along the sock and belt lines. Antihistamines are usually the only treatment required for insect bites; however, severe mosquito reactions (skeeter syndrome) may require prednisone. Applying insect repellent containing diethyltoluamide (DEET) 10% to 35% or picaridin 20% is the best method for preventing bites.