EPOW - Ecology Picture of the Week

This Beetle Gives You Blisters

Blister Beetle (Epicauta sp., cf. E. vittata), Family Meloidea
Oregon Oak Woodland, Columbia River Gorge, Oregon USA

Explanation:  Be careful when you handle this beautiful insect!  This is a blister beetle ... so-called because the common species of this family exude a substance called cantharadin from their knee joints and other body parts, which causes blisters when it comes in contact with the skin.  But it's not all bad.  In fact, cantharadin is extracted from the common European species of blister beetle (Lytta vesicatoria, also called the spanishfly) and is used as a medicinal drug to stimulate internal organs. 

Why does the blister beetle do this?  Cantharadin likely serves to thwart predators such as ground beetles and some birds, although other predators such as robber flies and mantids apparently are not harmed by it. 

Otherwise, adult blister beetles can be agricultural pests, feeding on beets, tomatoes, potatoes, and other crop products, as well as flowers and ornamentals ... but the larvae are seen as beneficial, as they feed on eggs of grasshoppers that themselves can be major agricultural pests in their adult form.  One larva blister beetle can consume 30 or more eggs, which is an entire egg pod for one grasshopper.  Other species of blister beetle feed on bee larvae in their nest.  

So which is it?  Helper or pest?  You decide.

The photos above show a blister beetle feeding on the base of blooms of this plant.  I don't know if the beetle is aiding in pollination of the plant or is avoiding pollen by going for the nectar at the base of each floret.  Blister beetles are known to feed on the flowers of many plant species, especially asters.   

Information:
     Borror, D. J., D. M. DeLong, and C. A. Triplehorn. 1976. An introduction to the study of insects. Fourth edition. Holt, Rinehart and Winston, New York. 852 pp.   
     Evans, A. V. 2008. Field guide to insects and spiders of North America. Sterling Publishing, New York. 497 pp. 
     Milne, L., M. Milne, and S. Rayfield. 1980. National Audubon Society field guide to North American insects and spiders. Alfred A. Knopf, New York. 989 pp.
     White, R. E. 1983. A field guide to the beetles of North America. Houghton Mifflin Co., Boston. 368 pp.