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Blister beetles are beetles (Coleoptera) of the family Meloidae, so called for their defensive secretion of a blistering agent, cantharidin. There are approximately 7,500 known species worldwide. Many are conspicuous and some aposematically colored, announcing their toxicity to would-be predators.
Cantharidin is a poisonous chemical that causes blistering of the skin. Cantharidin is used medically to remove warts and is collected for this purpose from species of the genera Mylabris and Lytta, especially Lytta vesicatoria, better known as "Spanish fly".
Blister beetles are hypermetamorphic, going through several larval stages, the first of which is typically a mobile triungulin. The larvae are insectivorous, mainly attacking bees, though a few feed on grasshopper eggs; while sometimes considered parasitoids, it appears that in general, the meloid larva consumes the immature host along with its provisions, and can often survive on the provisions alone, thus they are not obligatory parasitoids but rather food parasites that are facultatively parasitoid, or simply predatory. The adults sometimes feed on flowers and leaves of plants of such diverse families like Amaranthaceae, Asteraceae, Fabaceae, and Solanaceae.
The largest genus--Epicauta—contains many species that are toxic to horses. A few beetles consumed in a single feeding of alfalfa hay may be lethal. In semi-arid areas of the western United States, modern harvesting techniques may contribute to cantharidin content in harvested forage. The practice of hay conditioning [see Conditioner (farming)]--crushing the stalks to promote drying—also crushes any beetles present and causes the release of cantharidin into the fodder. Blister beetles are attracted to alfalfa and weeds during bloom. Reducing weeds and timing harvests before and after bloom are sound management tactics. Using equipment without hay conditioners may reduce beetle mortality and allow them to escape before baling.
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- Bhattacharjee, Pradip; Brodell, Robert T. (2003). "Cantharidin". In Robert T. Brodell and Sandra Marchese Johnson, eds. Warts: Diagnosis and Management—an Evidence-Based Approach. London: Martin Dunitz. pp. 151–160. ISBN 1-84184-240-0.
- University of Arizona VDL Blister Beetle Poisoning in Horses
- University of Colorado Extension Blister Beetles in Forage Crops