Blister beetles are insects known for producing a chemical that causes skin irritation and blistering. Belonging to the family Meloidae, they are named for this unique defense mechanism. Around 2,500 species exist worldwide, found in various environments.
Identifying Blister Beetles
Blister beetles are medium-sized, soft-bodied insects, 1 to 2.5 centimeters long. Coloration varies widely, including ash gray, black, bright yellow with black stripes, or metallic hues. They have an elongated, slender body with a broad head that appears wider than their narrow prothorax. Their wing covers are soft and flexible, sometimes leaving the abdomen partially exposed.
These beetles are found across the United States, particularly in the Atlantic and Gulf coasts, and also in Central and South America, Europe, Africa, and Asia. They inhabit gardens, fields, and agricultural areas, congregating on flowering plants where they feed on leaves, nectar, and pollen. Blister beetles are observed in areas with high grasshopper populations because their larvae feed on grasshopper eggs.
The Blistering Agent
The blistering effect is caused by a chemical compound called cantharidin. This odorless, colorless, oily substance is a naturally occurring terpenoid. Male blister beetles produce cantharidin, transferring it to females during mating as a copulatory gift. The female then uses this chemical to cover her eggs, providing defense against predators.
Cantharidin is released as a defensive mechanism when the beetle is crushed or disturbed. Upon contact with human skin, it acts as a vesicant, leading to irritation, swelling, and painful blisters within 24 to 48 hours. While skin exposure can be uncomfortable, the blisters are not life-threatening and resolve within a week to ten days. Ingesting cantharidin, however, is more hazardous, causing severe damage to the gastrointestinal and urinary tracts, and has been fatal in doses ranging from 10 to 65 milligrams in humans.
Safe Handling and First Aid
Avoid direct contact with blister beetles and never intentionally crush them. If a blister beetle lands on your skin, gently blow it away or carefully remove any clothing it has landed on without crushing the insect. Wash exposed skin thoroughly with soap and water immediately after contact to remove residual cantharidin. Any contaminated clothing should also be removed and washed.
If blisters form, clean them daily with warm, soapy water. A cold compress can reduce swelling and pain. While most blisters heal without complication, a healthcare provider may recommend topical steroid creams or antibiotics to manage symptoms and prevent secondary infections. Seek medical attention promptly if the reaction is severe, widespread, or if the eyes are affected, as cantharidin exposure to the eyes can lead to Nairobi eye. In cases of suspected ingestion, immediate contact with poison control is advised.