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Key Points

  • In addition to any focused or antidotal therapy available, aggressive symptom-based supportive care is important for all envenomations.

  • Knowledge of local venomous species may be helpful, although be aware that patients may have contact with nonlocal or exotic venomous animals.

  • North American venomous bites are rarely unprovoked.

  • Contact your local poison control center (1-800-222-1222) for assistance with diagnosing and managing all envenomations.


In 2010, there were more than 60,000 calls made to United States Poison Centers related to bites and envenomations. Although there are many venomous animal species in North America, a majority of these calls involved insects (including bees, wasps, hornets, and ants), arachnids (including spiders and scorpions), and snakes. From information provided in the 2010 Annual Report of the American Association of Poison Control Centers' National Poison Data System, there were a total of 5 fatalities related to all bites or envenomations and approximately 2,500 instances of antivenin being given.

The clinical presentations of the various forms of venom exposure vary greatly and are dependent on multiple factors including the species of the animal, the amount of venom delivered, and potential baseline medical problems in the envenomed patient. Patients presenting with an animal envenomation may therefore display a variety of symptoms ranging from local reaction to a bite or sting to generalized yet nonspecific effects (eg, vomiting, headache, hypertension) or toxin-specific findings (eg, paralysis or coagulopathy). This chapter focuses on the presentation, evaluation, and treatment of 2 of the most clinically relevant North American envenomations: snakes and spiders.


Venomous snakes found in North America are most easily divided into their 2 families: Elapidae and Viperidae (subfamily Crotalinae). The majority of venomous snakebites occurring yearly in North America are caused by snakes in the Crotalinae subfamily, which includes rattlesnakes (genus Crotalus), copperheads, and cottonmouths (genus Agkistrodon). Less than 5% of venomous snakebites are from the Elapidae family, which includes the coral snake. Fewer still may be from bites by exotic, nonnative snakes usually being kept as pets.

Venomous snakes found natively in North America are generally nonpredatory to humans. Bites, therefore, take place on provocation of the snake—either intentional or accidental. These bites are typically located on extremities, but particularly troublesome cases have been reported in which venomous bites have involved the face, neck, or tongue. The vast majority of venomous snakebites occur in young men, with an appreciable association with alcohol intoxication. Children are also at a higher risk for being bitten by a venomous snake.

There are a few characteristics that can help identify a North American snake as being part of the Crotalinae subfamily. These snakes have vertical slit-like pupils, long fangs, and a triangular head. This subfamily is also referred to as “pit vipers” because they have heat-sensing pits located on their heads just behind the ...

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