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Blister Beetles



Family: Meloidae

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About Blister Beetles

Blister beetles have been a common problem throughout the United States, particularly in Colorado, and are known to secrete a chemical called cantharidin. This chemical acts as a blistering agent when it comes in contact with skin and is damaging to humans and livestock. The blister beetle can also cause harm to other insects, preying on bee and grasshopper eggs.

Reproduction and Life Cycle

Each year blister beetles tend to have one generation. A female beetle can lay up to 4,000 eggs; however, many will not survive. The adults lay their eggs either in the soil or near a bee’s nest so that when the larvae hatch in the spring, they can attach themselves to bees or grasshoppers and feed off of their eggs (sometimes referred to as bee lice). From this larva stage, they will later turn into a legless grub, and then into a fully-grown adult, which occurs through May to September or the typical growing season. Depending on the specific variety of Blister Beetle will determine peak emergence periods.

Blister Beetles Identification and Habitat


Adult blister beetles are soft bodied and can grow between 3 and 20mm; however, they are commonly found to be 10 to 15mm long. The adults can be vivid in colour with striped or banded wing covers that are blue or metallic green and are flexible. However, they can also be a solid colour of either black or grey, or be yellow/orange and black striped. Their body is narrow and elongated in shape and has a leathery texture to it. They have a broad, rectangular-like shaped head.


Blister beetles feed on alfalfa and other blooming plants, which commonly place them in the field at the same time as harvest, mixing these toxic pests in with the forage and poisoning the livestock that eat it. Blister beetles also tend to be found in areas with frequent grasshopper outbreaks. While this beetle can damage a farmer’s alfalfa crop, especially when the beetle presents itself in swarms, the main concern is the effect they have on livestock, especially horses. When consumed, cantharidin can aggravate the animal’s urinary and gastrointestinal tracts, sometimes leading to fatalities.

Blister Beetles Management and Control Methods

Cultural Control

No parasites or predators have been discovered to control blister beetles. However, due to the fact that blister beetles tend to swarm towards alfalfa in its blooming stage, the best way to reduce the number of beetles in an alfalfa crop would be to cut the plant before the blooming occurs and get rid of any blooming weeds. If blister beetles are still located in the alfalfa, take off the windrower’s conditioner wheels to avoid squashing the beetles. If the beetles are killed in the process, this means livestock are more likely to ingest cantharidin since the beetles never had a chance to fly out of the dried hay. Additionally, blister beetles tend to gather along the fields edge, or close to the center in clusters. Therefore, when cutting hay, avoid these areas or separate the bales produced from these sections of the field.

Chemical Control

There are insecticides available for controlling blister beetle infestations in alfalfa. However, these management methods will only decrease the number of blister beetles present; it will not completely eliminate the pest. The beetle insecticide should be applied only a day before harvest to lessen the chances of new blister beetles entering the field. The killed beetles should fall to the ground and are unlikely to compromise the forage. Group 1 and Group 3 insecticides have been found to be effective on blister beetles. Common names: carboryl, lambda-cyhalothrin, and gamma-cyhalothrin. Make sure to read label directions for specific rates, intervals, precautions, and restrictions. To lessen the chance of killing bees in the process, do not apply when plants are in bloom. Keep in mind, blister beetles tend to only stay in a field for a short time; therefore, sometimes chemical treatment is not always advised as this will keep the dead beetles in the field, creating the possibility of them getting mixed into the hay.

Latin / Alternative Blister Beetles Names

  • - Meloidae