Blister Beetles

Facts, Identification & Control


Blister beetles are softbodied beetles that range in size from 1 to 2.5 cm in length. There are several species of blister beetle in the U.S. Adults range in color from an ash gray to bright yellow with black stripes. They usually are seen during the day on flowers and also are attracted to lights at night.

Behavior, Diet & Habits

Blister beetles belong to a group of insects with a very interesting and sordid past with people. They get their name from a caustic chemical they produce called cantharidin. When crushed, the beetle can literally bleed the chemical from its joints, and skin contact with it can result in blisters. Even though cantharidin is caustic, it has medical properties that people have long exploited in the form of Spanish fly. People would consume a concoction of dried and crushed blister beetles for ailments such as gout and arthritis, as well as using it as the aphrodisiac Spanish fly. Unfortunately, cantharidin can be fairly toxic and it is no longer widely used in medicine.

Blister beetles are not an indoor infesting pest. They tend to be more of an agricultural/livestock pest. Many species feed on plants which include ornamental and vegetable crops. Horses and livestock also may be affected. Blister beetles, feeding in a hay field, may accidentally be ground up when the hay is harvested. The cantharidin impregnates the hay and can be consumed by the animals, potentially resulting in their death.


Eggs are laid by the female in protected areas like under stones. The initial larvae are highly mobile and usually seek out insects such as bees as they feeds on flowers. The larvae ride back to the nest where they prey on the inhabitants of the nest. The larvae eventually become pupae and then transform into adults.

Signs of a Blister Beetle Infestation

Immature stages of blister beetles often go unnoticed. Adults, however, can be observed on vegetation.

More Information

Control of blister beetles typically does not involve an exterminator. As a mainly agricultural pest, most control is done when the crop is being grown or harvested. Growers should check crops for the presence of blister beetles, especially prior to harvesting. If blister beetles are present, a pesticide application can be used to control the beetles.

If a person or animal is suspected of consuming blister beetles, medical attention should be sought.

Blister Beetle Poisoning

Blister Beetle Larvae

Blister Beetle Bites