Blister Beetles in Montana: Species, Cantharidin Risk, and Safety

Blister Beetles (Meloididae) in Montana

Several species inhabit Montana, including the black blister beetle (Epicauta pensylvanica), margined blister beetle (E. pestifera), and spotted blister beetle (E. maculata). They are common in alfalfa fields and rangelands.

Cantharidin Hazard

• Beetles produce cantharidin, a potent vesicant (blistering agent).
• Contact causes skin blisters; ingestion (contaminated hay) can be fatal to horses and livestock.
• Horses are extremely sensitive: 4–6 grams of dried beetles can kill a 500 kg horse.

Prevention for Livestock Owners

1. Scout fields before cutting; avoid harvesting infested areas.
2. Use crimping/conditioning rollers to crush beetles (they fall out during drying).
3. Inspect hay; discard bales with visible beetles.
4. First-cutting hay often has fewer beetles.

Human Exposure

Rare; usually from handling beetles. Wash skin immediately; seek care if blisters are extensive or near eyes.