How Can I Control Blister Beetles?

Reader Contribution by Staff

We have a terrible problem with blister beetles — the gray ones with white stripes. They destroy our garden. We would like to find a chemical-free control. Can you help?

Blister beetles (Epicauta vittata and other closely related species) appear in swarms in summer, just as tomatoes, beans and other crops start looking good. This native species does one service — the larvae eat grasshopper eggs — but then the adults strip leaves from a dozen different plants. Hand-picking them can be dangerous, because a toxin in the beetles’ bodies can irritate the skin. Blister beetles often drop to the ground and play dead when disturbed, so the best way to collect them is to quietly sneak up and shake them into a pan of soapy water placed beneath the plants. Wear gloves to pick up any stragglers.

Some gardeners grow calendulas as a trap crop, or you can skip over a few pigweeds (Amaranthus species) when weeding and let them serve as blister beetle magnets. Old-time gardeners used pine branches to sweep the beetles into water-filled pits. If all else fails, spray infested plants with Monterey Garden Insect Spray, which contains spinosad, a biological pesticide made by fermenting a naturally occurring soil-borne bacterium. (A similar product, Entrust, is acceptable under organic certification guidelines, but it is not as widely available.) When using either form, the beetles should stop feeding soon after they eat some treated leaves, but nonleaf-eating beneficial insects will not be affected. If you cannot find it locally, you can buy Monterey Garden Insect Spray from

Barbara Pleasant, contributing editor