Blister beetles are long or cylindrical, soft-bodied or leathery, with broad, round or rectangular heads. The pronotum (just behind the head) is narrower than the head and the rest of the body. The wing covers are rounded curved around the body (not flattened). The antennae are threadlike or beaded.
Many species are black, brown, or other drab colors, sometimes with iridescent blues or bronzes or with yellow, orange, or red head, legs, or markings. Others are mostly yellow, orange, or red, sometimes with dark spots or stripes. When squeezed, blister beetles exude an irritating, oily chemical that can blister one’s skin.
The larvae go through several stages that look very different from each other. The grublike stages that parasitize underground bee nests are unlikely to be seen. The earliest stage, though tiny, is active; at this point, they have large heads and slender bodies, with functioning legs.
Length: less than ¼ to 2½ inches; most are ½ to ¾ inch (varies with species).
Habitat and Conservation
Adult blister beetles are often seen visiting flowers for food and mating opportunities. Several blister beetles prefer flowers in the sunflower family, which abound in prairies, old fields, pastures, along roadsides and other sunny places. But at least one species, for example, focuses on flowers of apple, plum, and other rose-family trees. Others spend more time on the ground, laying eggs in the soil.
Adults visit flowers to eat nectar, pollen, and sometimes entire flowers. Some species eat leaves. Different types of blister beetles prefer different plant families; most prevalent are plants in the sunflower, bean, and potato families. The larvae of most blister beetles are parasitic on ground-nesting, solitary bees, eating the pollen, nectar, and honey stored for the bee’s young, plus the eggs and young themselves. The larvae of some groups eat the egg clusters of grasshoppers.
Common. The adults of some species feed on crops, including potatoes, tomatoes, clover, and others, and in large numbers can be serious agricultural pests. The larvae of some species, however, can help agriculture by eating grasshopper eggs, thus reducing populations of those crop eaters. The larvae of other blister beetles parasitize bees, limiting populations of pollinators.
Blister beetles have unusual larvae. The egg, attached to flowers (or somewhere else where a bee will visit), hatches into an active larva called a triungulin, with well-developed legs, antennae, and the wherewithal to grab onto a visiting bee. The bee unknowingly carries it to its nest, where the larva molts and becomes a pudgy, sedentary grub that eats the honey, eggs, and/or larvae of the host bee, then pupates and becomes an adult blister beetle.
The cantharidin that causes skin to blister is used to make medicine for removing warts. A European species, Lytta vesicatoria, is the beetle from which the poisonous antique aphrodisiac “Spanish fly” was obtained. Horses have died from eating hay containing dead blister beetles.
Blister beetles have fascinating interactions with other insects. As tiny larvae, they must hitch a ride to the right kind of bee’s nest, then parasitize it until mature. Other insects, immune to the toxic oil, lick or rub against blister beetles to acquire the defensive chemical for themselves.