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Blister beetle, common name for the 2,000 species of the family Meloidae (order Coleoptera). These insects secrete an irritating substance, called cantharidin, which is collected mainly from Mylabris and the European species Lytta vesicatoria, commonly called the Spanish fly; cantharidin is sold commercially for medical purposes. In the past, when inducing the formation of blisters was a common remedy for many ailments, cantharidin was often used. It was also a major ingredient in love potions. Blister beetles are both helpful and harmful to man. The larvae eat grasshopper eggs, but the adults destroy crops.
Adult blister beetles are often brightly coloured, the need for camouflage being eliminated by their ability to secrete cantharidin. They range between 3 and 20 millimetres (0.1 to 0.8 inch) in length, the majority between 10 and 1 5 millimetres. The long, slender, leathery bodies are covered by metallic green or blue wing covers, often marked with bands or stripes.
The female lays between 3,000 and 4,000 eggs; only a few survive, however, because of the complicated and haphazard life history (hypermetamorphosis). The female of Sitaris muralis deposits masses of eggs near solitary bees’ nests. The larvae hatch from the eggs and remain dormant throughout the winter.
In the spring, tiny active forms (triungulins), sometimes called bee lice, attach themselves to bees. They feed on eggs and stored food in the hive as they pass through several more developmental stages, changing from a larva to a legless grub. When the pupal stage is complete, the newly emerged adult drops to the ground and begins feeding on cultivated plants.
The female of some blister beetles (e.g., Epicauta vittata) deposits masses of eggs either on or in the ground. The triungulin feeds on grasshopper eggs, undergoes a series of molts, and spends the winter in a pupa-like stage. After passing through several more larval stages and a true pupal stage, the adult blister beetle emerges.
The members of the subfamily Meloinae are sometimes called oil beetles, They do not have hindwings as do most blister beetles, nor do their wing covers meet in the middle of the back; rather, they are much shorter and overlap. Oil beetles secrete an oily substance that protects them because of its bad taste. In some species the forceps-like antennae of the male are used to hold the female during mating. An oil beetle genus common in both Europe and North America is Meloe.
