Although there are more members of the Coleoptera or beetle family than any other arthropod, the only ones with clinical significance for envenomation in humans are blister beetles. Blister beetles (families Staphylindae and Meloidae) are found throughout the United States, and include beetles known as Spanish fly ( Lytta vesicatoria).1 When disturbed or crushed on the skin, they exude a vesicating agent called cantharidin from the joints of their legs or from their bodies that can penetrate the epidermis to produce irritation and blistering within a few hours of contact. If ingested, cantharidin can produce intense gastrointestinal disturbances with symptoms of nausea, vomiting, diarrhea, and abdominal cramps.20 Initial contact with the beetle produces a burning, tingling sensation and a mild rash. Within a few hours, flaccid, elongated vesicles and bullae develop from a few millimeters to several centimeters in diameter. Blebs erupt 2 to 5 h after contact and can be hemorrhagic and painful. A severe chemical conjunctivitis can occur if cantharidin contacts the eyes from contaminated hands.
Treatment consists of protecting the bullae from secondary infection with an occlusive dressing. Large bullae should be drained and an antibiotic ointment applied. Bullae occurring on the feet should be managed with wet dressings applied for 24 to 48 h. Application of steroid creams to blebs may be helpful. Lesions usually resolve in 2 to 3 days.
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