Alphabetical List of Critters - Blister Beetles
Blister beetles belong to a family of beetles called Meloidae. Many of them are showy and some have warning coloration that signals to potential predators to stay away, because they contain a chemical in their hemolymph called cantharidin, which is an odorless blistering agent that will cause temporary blisters when it comes into contact with human skin; hence, the name for these beetles. The beetles release the substance (i.e. the cantharidin) when they are pressed or rubbed, as a defense mechanism, but careful, light handling of them rarely leads to blistering unless the cantharidin comes into contact with more sensitive areas on the body, where the skin is thinner, such as the areas between one’s fingers. The beetles are attracted to lights at night, so that is one common way by which they are encountered by people, leading to blisters on the neck and arms as the beetles are swatted or squished from the annoyance of their presence. Cantharidin collected from species of two genera, Mylabris and Lytta, is actually used medically to remove warts.
The blister beetle genus Epicauta is highly toxic to horses. A few beetles consumed in a single feeding of alfalfa can be fatal.
Blister beetle larvae are predators of other insects, mainly attacking bees (latching onto them from atop flowers). The adults, which tend to come together in groups (i.e. they are gregarious), feed on flowers and leaves of plants of diverse families like Amaranthaceae, Asteraceae, Fabaceae, and Solanaceae, causing extensive defoliation sometimes, where they happen to be congregated.
Detailed Fact Sheet: Blister Beetles (University of Florida)