The adult European Spanishfly is shiny green, sometimes tinged with reddish yellow. It has a soft, elongated body, 12 to 21 mm (0.47 to 0.88 in) long. Like other blister beetles, the thorax, or neck, is narrow, and the head is commonly wider than the body. They are herbivores, feeding chiefly on pollen and petals of ash, lilac, and privet.
Eggs are laid in batches in shallow burrows in soil. The emergent larvae, known as triungulins, are active predators. They seek nests of ground-dwelling bees and kill and consume the bee larvae. Triungulins have a broad head and thorax, well-developed legs and antennae, and a pair of tail filaments called cerci.
Blister-beetle larvae develop by hypermetamorphosis: Each growth stage, or instar, is different in appearance and habits. The head and appendages of the second through fifth instars become reduced in size with each molt. The abdomen becomes more robust, with indistinct segments, and later stages do not feed. Sixth instars are greatly reduced in size and become inactive pseudopupae, from which adults emerge in spring. Spanishfly has one generation each year.
Spanishfly has been harvested for its extract for over 2000 years. The beetles are shaken onto cloths from the bushes and trees where they feed. Then they are killed in boiling water or vinegar, dried in the sun or in ovens. Cantharidin obtained from the dried, crushed bodies of Spanishfly and mixed into various medicines has been used as a salve, diuretic, and aphrodisiac. The ancient Greeks and Romans also used it as a poison. Cantharidin is still used today as an ingredient in remedies for urogenital disorders. Its benefits as a sex stimulant have been largely discredited.
Some other species of blister beetles in the Spanishfly genus are pests because they eat crops or their bodies contaminate harvested fodder. For example, adults of the Nuttall blister beetle feed on alfalfa and other legumes; their bodies commonly poison horses and other livestock that eat the beetle-infested crop.
Scientific classification: Spanishfly beetles belong to the genus Lytta of the family Meloidae. The European Spanishfly is classified as Lytta vesicatoria; the Nuttall blister beetle is classified as Lytta nuttalli.