Understanding the Two Main Types of Animal Venom

Poison secreted by animals is called venom. Animals produce venom through specialized glands often associated with teeth, spines, or stingers.

Venom may serve a purely defensive purpose, or it may help in capturing prey. Some venoms also function as digestive fluids.

There are two types of animal venom. A neurotoxin (New Latin for "nerve poison") acts on the victim's nervous system, causing excitation (cramps, vomiting, convulsions) or depression (paralysis, respiratory or cardiac depression or arrest). A hemotoxin ("blood poison") breaks down the victim's tissues, usually by an acid or a toxin that prevents or causes blood clotting, or destroys red or white blood cells. Venom usually contains both types, but one dominates.

Many major groups of animals contain venomous species, including various fish, lizards, scorpions, snakes, and spiders. Here are some examples.

black widow spider
The black widow spider is found throughout the world, with three species living in the United States. The female, which is shiny black with an hourglass-shaped red mark on the underside of the abdomen, often kills and eats the male after mating, hence the spider's name. It uses a neurotoxic venom that is about fifteen times more toxic than that of a rattlesnake. In humans, the bite causes severe nausea, vomiting, and paralysis, but, because the spider contains only a tiny quantity of venom, the result is rarely fatal.

brown spider
The brown spider is found in Europe, Asia, and the Americas. It uses a hemotoxic venom that destroys the walls of blood vessels near the site of the bite, often resulting in pain, bleeding, blistering, and ulceration. Sometimes the venom causes fever, vomiting, convulsions, and fatal heart attack.