Technically known as a blister beetle, a blister bug is an insect that produces chemicals that can burn skin and produce blisters. Many different species of the bug exist all over the world. Typically, they feed on vegetative crops and can occur in large groups. The burning chemical, cantharidin, is poisonous to animals, and acts as a deterrent to animals who might otherwise eat them.
Scientists classify animals and insects into groups depending on how related they are to each other. Each blister bug is of a particular species; for example, Epicuata vittata. Groups of species then fall into genus groups, such as Epicuata or Lytta. Collections of all the genera, which is the plural of genus, fall into the family Meloidae.
Over 2,500 species of blister bug are included in the Meloidae family. Even though the beetles live all over the world, they all contain a chemical called cantharidin. Some insects only produce a stinging or poisonous chemical from specialized glands, and release them only in certain situations, such as directly at a potential attacker.
A blister bug does not release cantharidin deliberately. Instead, it has the chemical inside its body, running through the tissues and blood of the insect. The presence of this blistering substance is not useful for an individual beetle, faced with a predator that wants to eat it, or a situation where the beetle is going to be squashed. Throughout the species' evolution, however, the unpleasant and dangerous burn from the chemical teaches animals and humans to avoid it. The species then have less risk of being eaten.
Sometimes, however, the beetles suffer predation or accidental crushing or touching. When the adult is squashed, or a human, for example, touches them in a manner which scares the beetle, then the cantharidin comes out of the body and burns the skin. Typically, the adult beetles feed on plants, and animals may accidentally eat them during grazing. Just one beetle is capable of killing an animal, and as the cantharidin persists in the bug even after death, the beetle need not be alive to kill an animal.
Visually, a blister bug has a cylinder-shaped body, and an obvious neck between the body and the head. They come in a variety of colors, from dull brown to stripy yellow. Often, the bugs group together in swarms where food is present. The adults are agricultural pests, but the immature forms may be useful as pest controllers, because they eat the eggs of grasshoppers and crickets.