Description:

Blister beetles vary by species in shape, size (3/8 to 1 inch long) and color (solid gray to black or with paler wing margins, metallic, yellowish striped or spotted). Most are long, cylindrical narrow-bodied beetles that have heads that are wider than the first thoracic segment (pronotum). The wing (elytra) covers are usually soft and pliable.

Life Cycle:

Winter is spent in later larval stages and pupation occurs in the spring. The pupal stage lasts about 2 weeks and adults appear in early summer. Female beetles lay clusters of eggs in the soil. The first stage (instar) larva hatching from the egg (triungulin) is a tiny, active, long-legged larva that seeks the appropriate host. Once there, the larva develops through a number of stages, each with progressively reduced appendages and increasingly grub-like in appearance. The first number of larval stages develop within about month, but the second to the last (pseudopupa) can remain for about 230 days before molting into the last (sixth) larval stage in the spring. Generally, one generation occurs per year although some develop in 35 to 50 days while in others, development takes 3 years.

Pest Status:

Adults usually occur in loose groups or swarms that feed on leaves of certain plants, especially legumes. Their bodies contain a toxin (cantharadin) that can cause blisters to form on the skin. Animals, particularly horses, ingesting beetle contaminated feed become extremely ill and may die. Handling blister beetles can cause blisters on the skin as a reaction to cantharadin. Larval stages feed on grasshopper eggs or are predaceous and are thus considered to be beneficial, although a few species feed in nests of solitary bees.

Control:

Control of blister beetles requires vigilant scouting and good management skills. The critical problem of blister beetle poisoning develops when large swarms of adult beetles are incorporated in the hay during the harvesting process. Adults are very mobile and may move from one area of the field to another in a short period of time.