- Related Topics:
- strepsipteran
- Spanish fly
- oil beetle
- cantharides
blister beetle
blister beetle, (family Meloidae), any of approximately 2,500 species of beetles that secrete an irritating substance known as cantharidin. Blister beetles are both helpful and harmful to humans. The larvae of some species help control grasshopper populations by feeding on their eggs, and certain blister beetles are even cultivated as the source of cantharidin, which is used in pharmaceuticals and traditional remedies. At the same time, large numbers of adult blister beetles can destroy crops and the insects pose a risk to livestock who eat contaminated hay.
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Coleoptera
- Family: Meloidae
See also list of beetles.
Physical description
Adult blister beetles are often brightly colored in solids, stripes, or spots, the need for camouflage being eliminated by their ability to secrete blistering cantharidin. They range between 3 and 20 mm (0.1 to 0.8 inch) in length, with the majority between 10 and 15 mm (0.4 and 0.6 inch). Their long, slender, cylindrical, leathery bodies are often covered by metallic green or blue elytra (wing covers), often marked with bands or stripes. They have long, segmented antennae.
The members of the subfamily Meloinae are sometimes known as 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, the covers are much shorter and overlap. Oil beetles secrete an oily substance that protects them from predators because of its bad taste. In some species the forcepslike 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.
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Natural history
The female lays between 3,000 and 4,000 eggs; only a few of the young survive. Blister beetles have a complicated and seemingly haphazard life history, known as hypermetamorphosis, meaning they have different larval types in different instars (the stages between molts). The early larval stages, known as triungulins, usually are active, and the later stages are parasitic on other organisms. Adults are typically herbivores and eat floral parts and sometimes foliage.
For example, the female of Sitaris muralis deposits masses of eggs near solitary beesâ nests. The larvae hatch from the eggs and remain dormant throughout the winter. In the spring tiny triungulins, sometimes known as bee lice, attach themselves to a bee. They feed on eggs and stored food in the bee nest 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.
Similarly, 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 (periodic shedding of skin), and spends the winter in a pupallike stage. After passing through several more larval stages and a true pupal stage, the adult blister beetle emerges.
Cantharidin
Cantharidin is used by blister beetles for defense and is released from the mouths and leg joints when the insects are crushed, threatened, or handled. The substance is collected mainly from Mylabris and the emerald green European species Lytta vesicatoria, commonly called Spanish fly. Sometimes known as beetlejuice, cantharidin is used medically as a topical skin irritant to remove warts and molluscum. Given that inducing blisters has been a common remedy for many ailments, cantharidin has a long history of use in traditional medicine and is applied as an exfoliating agent and to treat rheumatism. Esteemed as an aphrodisiac, it is been a major ingredient in so-called love potions.
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Considered a burn agent, cantharidin is poisonous in large doses and can cause kidney damage and death in humans and other animals. Horses and other livestock have been fatally poisoned by consuming blister beetles in hay.