Blister beetle

Blister beetle; Temporal range: Cenomanian–Recent PreꞒ Ꞓ O S D C P T J K Pg N
	Hycleus lugens
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Superfamily:	Tenebrionoidea
Family:	Meloidae; Gyllenhaal, 1810
Subfamilies
	Eleticinae; Meloinae; Nemognathinae; Tetraonycinae

Blister beetles are beetles of the family Meloidae, so called for their defensive secretion of a blistering agent, cantharidin. About 7,500 species are known worldwide. Many are conspicuous and some are aposematically colored, announcing their toxicity to would-be predators.

Description

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, in general, the meloid larva apparently consumes the immature host along with its provisions, and can often survive on the provisions alone; thus it is not an obligatory parasitoid, but rather a facultative parasitoid, or simply a kleptoparasite. The adults sometimes feed on flowers and leaves of plants of such diverse families as the Amaranthaceae, Asteraceae, Fabaceae, and Solanaceae.^[1]

Female margined blister beetle pursued by multiple males.

Cantharidin, a poisonous chemical that causes blistering of the skin, is secreted as a defensive agent. It is used medically to remove warts^[2] and is collected for this purpose from species of the genera Mylabris and Lytta, especially Lytta vesicatoria, better known as "Spanish fly".

Toxicity

Cantharidin is the principal irritant in "Spanish fly", a folk medicine prepared from dried beetles in the family Meloidae.

The largest genus, Epicauta, contains many species toxic to horses. A few beetles consumed in a single feeding of alfalfa hay may be lethal.^[3] In semiarid areas of the western United States, modern harvesting techniques may contribute to cantharidin content in harvested forage. The practice of hay conditioning, 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 practices. Using equipment without hay conditioners may reduce beetle mortality and allow them to escape before baling.^[4]

Evolutionary history

The family is thought to have begun diversifying during the Early Cretaceous. The oldest fossil of the group is a larva (triangulin) found phoretic on a schizopterid bug from the mid Cretaceous Burmese amber, dated to around 99 million years ago.^[5]