Over 5000 Americans suffer snake bites annually, and of these, nearly one quarter are from poisonous species. Although these cases are undeniably underreported, death appears to occur in only a few cases each year,<sup>75 Litovitz T.L., Felberg L., White S. , e al. 1995 annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System Am J Emerg Med 1996 ;  14 : 487  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> and often reflects delay in obtaining medical care.<sup>47 Hardy D.L. Fatal rattlesnake envenomation in Arizona: 1969–1984 J Toxicol Clin Toxicol 1986 ;  24 : 1  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> Two families of venomous snakes indigenous to the United States account for most envenomations: (1) Crotalidae (pit vipers or new world vipers) and (2) Elapidae. Elapids are brightly colored and have front, fixed-fanged snakes, that inhabit the southeastern and southwestern United States. They are responsible for less than 0.5% of the envenomations that occur<sup>104 Parish H.M., Golden J.C., Silverberg S.L. Comparison between snakebites in children and adults Pediatrics 1965 ;  36 : 251

Cliccare qui per andare alla sezione Riferimenti</sup> and are not discussed further. The focus of this article is on the snakes of the family Crotalidae (Table 1)

Crotalids possess triangular-shaped heads, elliptical-shaped pupils during daylight, and a single row of subcaudal scales. They also possess infrared heat-sensing pits, thus the name “pit viper,” which enable them to locate prey, guide the direction of strike, and possibly determine the amount of venom to be released.<sup>10 Bullock T.H., Diecke F.P.J. Properties of an infrared receptor J Physiol 1956 ;  134 : 47

Cliccare qui per andare alla sezione Riferimenti</sup> Three genera of crotalids inhabit the United States: (1) Crotalus, (2) Sistrurus, and (3) Agkistrodon. Members of the genera Crotalus and Sistrurus possess rattles on their tails and are collectively referred to as rattlesnakes. The rattleless members of Agkistrodon comprise cottonmouths (water moccasins) and copperheads (Figure 1)