Recognizing venomous snakes

February 27, 2012, 11:50 pm

Coral snake

★★★½☆

Recognizing Dangerous Snakes in the United States and Candada: A Novel 3-Step Indentification Method. Cardwell MD. Wilderness Environ Med 2011 Dec;22:304-308.

Abstract

This paper presents a 3-step flowchart that can identify with reasonable accuracy poisonous snakes (crotalids or elapids) in the United States or Canada. The identification system uses features on the body of the snake, not the head, since handling decapitated heads or dead snakes with intact heads can be dangerous. Decapitated snake heads can still bite.

The identification scheme depends on examining the snake’s carcass to determine if there are colored rings that completely encircle the body, if the dorsal midline scales are keeled, and if the proximal sub caudal scales are undivided or divided. (To see illustrations of some of these findings, click here.)

This scheme can be useful if a patient brings the body of a dead snake into the emergency department. However, the authors emphasize a number of important caveats:

  • Although headless carcasses are safe to handle, freshly killed snakes and severed heads can cause envenomation through reflexive biting.
  • Live snakes should be kept out of ambulances and emergency rooms.
  • If a live snake is brought in some sort of container, the risk of trying to identify it outweighs any potential benefit.
  • At all times keep greater than one snake-length away from a live snake.
  • The identification scheme presented in this paper should NOT be used outside of the United States or Canada, since snake characteristics can vary in other locations.

There is an old mnemonic that was devised to help identify poisonous snakes (specifically, coral snakes): “Red on yellow, kill a fellow; red on black, venom lack.” You can see that by following this mnemonic it is clear the snake pictured above is venomous.  There are several problems with this mnemonic. One, it presumes a certain proximity to the snake that may be unwise. Second, it is not valid in Latin American or South America, where venomous snakes have different colorations.  I’ve come up with a revised — and I think better — mnemonic: “Red on yellow, run like hell; red on black, run like hell.” This is valid both in the Northern and Southern hemispheres.

[Photograph of coral snake from Wikipedia.org]

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