Poisonous and nonpoisonous snakes are widely distributed throughout North America. Ninety percent of snakebites in dogs involve the head and legs. In the United States there are four types of poisonous snakes: cottonmouths (also called water moccasins), rattlesnakes, copperheads, and coral snakes. The diagnosis of poisonous snakebite is made by the appearance of the bite, the behavior of the animal, and your identification of the species of snake. In general, bites of nonpoisonous snakes do not cause swelling or pain. They show teeth marks in the shape of a horseshoe, but no fang marks.
You can identify these species by their large size (4 to 8 feet, 1.2 to 2.4 m, long), triangular heads, pits below and between the eyes, elliptical pupils, rough scales, and the presence of retractable fangs in the upper jaw.
The bite: You may see one or two bleeding puncture wounds in the skin; these are fang marks. These marks may not be visible because of the dog’s coat. The pain is immediate and severe. The tissues are swollen and discolored due to bleeding at the site of the bite.
Note that 25 percent of poisonous snakebites lack venom and thus do not produce a local reaction. While absence of local swelling and pain is a good sign, it does not guarantee the dog won’t become sick. Severe venom poisoning has been known to occur without a local reaction.
The dog’s behavior: Signs of envenomation may take several hours to appear because of variables such as time of the year, species of the snake, toxicity of the venom, amount injected, location of the bite, and size and health of the dog. The amount of venom injected bears no relationship to the size of the snake. Signs of venom poisoning include extreme restlessness, panting, drooling, vomiting, diarrhea, uncoordinated gait, respiratory depression, shock, and sometimes death.