fever blister: see herpes simplex.

blister rust: see rust.

blister gas: see poison gas.

blister beetle, common name for certain soft-bodied, usually black or brown, mostly elongate and cylindrical beetles belonging to the family Meloidae. Blister beetles are common insects found feeding on the flowers and foliage of various plants. Occasionally some, e.g., potato beetles, become serious defoliating pests of potatoes, tomatoes, beets, asters, and other crops and flowers. The larvae are predacious or parasitic, feeding on the eggs of grasshoppers and of bees. Blister beetles undergo hypermetamorphosis, a complex life cycle with several different larval forms. The first of the six larval stages, called a triungulin, is a minute, active, and long-legged form that seeks out the host's nest; the following stages are grublike. Adults emerge in midsummer. One group of blister beetles has body fluids that contain cantharadin, a substance that can cause the skin to blister, from which the family gets its name. The Spanish fly (Lytta vesicatoria), a bright green or bluish blister beetle, is a common S European species from which cantharides are extracted and commercially prepared by crushing the wing covers (elytra) of the adults. This quite poisonous chemical is used medicinally as a skin irritant (in plasters), a diuretic, and an aphrodisiac. The lethal dosage for man is about .03 grams. Another group of meloid beetles has no cantharadin and is sometimes called the oil beetles because of the oily substance they secrete as protection against predators. Blister and oil beetles may be brushed into pans of kerosene or killed with systemic poisons or contact insecticides. Blister beetles are classified in the phylum Arthropoda, class Insecta, order Coleoptera, family Meloidae.

blister, puffy swelling of the outer skin (epidermis) caused by burn, friction, or irritants like poison ivy. A response of the body to protect deeper tissue, blisters generally contain serum, the liquid component of blood. The so-called blood blister, however, forms over ruptured capillaries and therefore contains whole blood.

Any of approximately 2,000 species of beetles (family Meloidae) that secrete an irritating substance, cantharidin, which is used medically as a topical skin irritant to remove warts. In the past, cantharidin was often used to induce blisters, a common remedy for many ailments, and the dried remains of Spanish fly (Lytta vesicatoria) were a major ingredient in so-called love potions. Adult blister beetles, which are often brightly coloured, range between 0.1 and 0.8 in. (3–20 mm) in length. Blister beetles are both helpful and harmful to humans; the larvae eat grasshopper eggs, but the adults destroy crops.

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Rounded skin elevation in which fluid fills a separation between layers of epidermis or between the epidermis and the dermis. The fluid is usually clear; yellowish fluid contains pus, and red fluid contains blood. Blisters often occur on the palms or soles when pressure and friction cause an upper skin layer to move back and forth over the one under it. A small gap opens between them and becomes filled with fluid. This type generally heals spontaneously, sometimes leaving a thickened callus. Blisters that occur as symptoms of contact dermatitis, viral infection, or autoimmune disease can appear anywhere on the body and may leave scars.

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