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Snakebite Facts

  • 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 venomous. About 25 species of venomous 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.

Venomous Snakes Most Dangerous to Humans

Two major families of snakes account for most venomous snakes dangerous to humans.

1. The elapid family includes:

  • the cobras (Naja and other genera) of Asia and Africa;
  • the mambas (Dendroaspis) of Africa; the kraits (Bungarus) of Asia;
  • the coral snakes (Micrurus) of the Americas; and the Australian elapids, which include the coastal taipan (Oxyuranus scutellatus),
  • tiger snakes (Notechis), king brown snake (Pseudechis australis), and
  • death adders (Acanthophis).
  • Highly venomous sea snakes are closely related to the Australian elapids.

Snakes from the elapid family

King cobra (Ophiophagus hannah), a dangerous Asian elapid and longest of the venomous snakes at around 4 m (13 ft). 

Black mamba (Dendraspis polylepis), an extremely fast, large, and dangerous African elapid. 

Coral snake (Micrurus fulvius), a shy American elapid that accounts for only about 1% of venomous snakebites in the United States. Recognize it by this catch phrase: "Red on yellow, kill a fellow." 

Milk snake (Lampropeltis triangulum), a harmless mimic of the coral snake. "Red on black, venom lack," although this old saying becomes unreliable south of the United States. 

2. The viper family includes:

  • the rattlesnakes (Crotalus) (Western diamondback rattlesnake and timber rattlesnake), moccasins (Agkistrodon), and lance-headed vipers (Bothrops) of the Americas;
  • the saw-scaled vipers (Echis) of Asia and Africa;
  • the Russell's viper (Daboia russellii) of Asia; and
  • the puff adder (Bitis arietans) and Gaboon viper (Bitis gabonica) of Africa.

Snakes from the viper family

Western diamondback rattlesnake (Crotalus atrox), an American pit viper, with rattle vibrating. This is one of the most dangerous snakes of North America. 

Timber rattlesnake (Crotalus horridus), American pit viper, caught yawning after a big meal.

Cottonmouth or water moccasin (Agkistrodon piscivorous), American pit viper usually found in or near water.

Northern copperhead (Agkistrodon contortrix), an American pit viper. Bites by this species tend to be less severe than rattlesnake or water moccasin bites but still require urgent medical attention.

Most species of the most widely distributed and diverse snake family, the Colubrids, lack venom that is dangerous to humans. Some species, however, including the boomslang (Dispholidus typus), twig snakes (Thelotornis), the Japanese garter snake (Rhabdophis tigrinus), and brown tree snake (Boiga irregularis), can be dangerous. Other members of this family, including American garter snakes, kingsnakes, rat snakes, and racers, are harmless to humans.

Medically Reviewed by a Doctor on 11/20/2017

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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.


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