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Snakebite Overview

Patient Comments

Snakes are remarkable animals, successful on land, in the sea, in forests, in grasslands, in lakes, and in deserts. Despite their sinister reputation, snakes are almost always more scared of you than you are of them. Most snakes do not act aggressive toward humans without provocation.

Snakes are meat eaters and they catch prey that includes insects, birds, small mammals, and other reptiles, sometimes including other snakes. Only about 400 of 3,000 snake species worldwide are poisonous. About 25 species of poisonous snakes are found in North America. Many snakes kill their prey by constriction. In constriction, a snake suffocates its prey by tightening its hold around the chest, preventing breathing or causing direct cardiac arrest. Snakes do not kill by crushing prey. Some snakes grab prey with their teeth and then swallow it whole.

Snakes are cold-blooded. Thus, they are unable to increase their body temperature and stay active when it is cold outside. They are most active at 25-32 C (77-90 F).

The Bite

Poisonous snakes inject venom using modified salivary glands. During envenomation (the bite that injects venom or poison), the venom passes from the venom gland through a duct into the snake's fangs, and finally into its prey. Not all bites lead to envenomation. Snakes can regulate whether to release venom and how much to release. "Dry Bites" (a bite where no venom is injected) occur in between 25%-50% of snake bites. This variation is species specific with approximately 25% of pit-viper bites being "dry" and up to 50% of coral snake bites. Snake venom is a combination of numerous substances with varying effects.

In simple terms, these proteins can be divided into 4 categories:

  1. Cytotoxins cause local tissue damage.
  2. Hemotoxins cause internal bleeding.
  3. Neurotoxins affect the nervous system.
  4. Cardiotoxins act directly on the heart.

The number of bites and fatalities varies markedly by geographic region. Reporting of snakebites is not mandatory in many areas of the world, making it difficult to determine the number of bites. Many articles are based on population models with multiple assumptions leading to a wide range of statistical reporting. Snakebites are more common in tropical regions and in areas that are primarily agricultural. In these areas, large numbers of people coexist with numerous snakes. Very few deaths occur per year from snakebites in the United States. People provoke bites by handling or even attacking snakes in a significant number of cases in the United States.

Medically Reviewed by a Doctor on 12/9/2014

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Snake and Lizard Bites

Poisonous snake or lizard bite

A bite from a poisonous (venomous) snake or lizard requires emergency care. If you have been bitten by a snake or lizard that you know or think might be poisonous, callor other emergency services immediately. Do not wait for symptoms to develop.

If you are not sure what type of snake or lizard bit you, call the Poison Control Center immediately to help identify the snake or lizard and find out what to do next. Medicine to counteract the effects of the poison (antivenom) can save a limb or your life.

It is important to stay calm.

Poisonous snakes or lizards found in North America include:

  • Pit vipers (family Viperidae), such as the rattlesnake, copperhead, and water moccasin (also called cottonmouth).
  • Coral snake (family Elapidae).
  • Gila monster and Mexican beaded lizard.

Maine, Alaska, and Hawaii are the only states that don't have at least one poisonous snake species in the wild.


Read What Your Physician is Reading on Medscape

Snakebite »

Most snakebites are innocuous and are delivered by nonpoisonous species.

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