Blister Beetles: What to Know

Medically Reviewed by Jabeen Begum, MD on January 13, 2023
Written by Alyssa Anderson
5 min read

Insects become pests for a number of reasons. They can invade your home, eat your plants, and endanger your family’s health. Blister beetles are an example of a pest that’s dangerous to both your health and your crops. 

Blister beetles can cause serious injuries when they’re mishandled. Make sure you know how to identify these insects so you can handle them safely and effectively.

Blister beetles are insects from the biological family Meloidae. This family includes at least 120 genera, or groups, and over 2,500 species. They all behave in similar ways and have similar body types. Importantly, they can all impact your health in the same way by producing a chemical that creates blisters on and within your body. 

People used to eat certain species of blister beetles as aphrodisiacs. But this is the most dangerous way to interact with them. 

Make sure that you know how to identify these beetles so you can avoid touching and eating them, which may lead to serious health problems.

What do blister beetles look like? Blister beetles can be in different colors, body shapes, and sizes. They have soft, oval-shaped bodies, long legs, and unusually narrow necks.  

The species can range in size from 0.39 inches to 0.98 inches. 

Some are brightly colored, but some can also be black, brown, or gray.  

What’s the blister beetle life cycle? The blister beetle life cycle depends on the species. Progression through their life cycles can also depend on the environment. 

Most species of blister beetle have four main stages in their life cycles: 

  • Egg 
  • 1st grub phase — a type of larval stage with multiple instars (stages)
  • 2nd grub phase — a type of larval stage with multiple instars (stages)
  • Adult

The eggs are laid in clusters in leaf litter and the bark of trees. Humans rarely see larval stages of blister beetles because most of them invade specific types of bees’ nests. 

This means that the adult stage is the only problematic pest stage for the blister beetle. 

What do blister beetles eat? All species of blister beetle rely on plants for food. The majority of species only eat flowers, but some also devour leaves. 

Certain blister beetles become expensive pests in the agricultural industry. They’re capable of quickly eating all of the leaves on valuable crops. This includes: 

There are too many species of blister beetle to list all of them here. You can find at least 26 different species in Florida alone. Two species that are particularly problematic for U.S. crops are described below. 

Epicauta funebris. This is the margined blister beetle. They’re found on the east coast and as far west as Texas. They have black bodies, legs, and wings. A white line rings each of their wings. 

Epicauta vittata. This is the striped blister beetle. This species is found in Canada and all U.S. states. Their heads, bodies, and wings are golden-brown with black stripes.

You can find many blister beetles species in the Atlantic and Gulf coasts of the U.S. Some species are also found throughout: 

  • The West Indies
  • South America
  • Central America
  • Europe
  • Africa
  • Asia

In your yard, you’ll most likely find them hanging out on the flowers of their food plants. They’re also very attracted to artificial lights in the dark.

Blister beetles don’t invade homes. The first sign that you have a local problem may be when you swat one and develop blisters. 

Otherwise, you may see them living on and feeding from your crops. Check for beetles on leaves and flowers — especially if you notice a lot of holes in your plants.

Blister beetles live in places where they can find both food and the right bee species for their larvae to prey on. If there are a lot of them in your yard, then they likely favor your local environment. 

Are blister beetles dangerous? Most blister beetle encounters aren't life-threatening. However, there are also reports of human poisonings. 

Blister beetles produce a harmful chemical called cantharidin. Cantharidin is a colorless, odorless terpene (a compound usually found in plants). It oozes from the beetles’ bodies when they’re squished or rubbed.  

Cantharidin causes blisters to form on your body when it comes in contact with your skin. It also causes symptoms when it comes in contact with your mucus membranes. These include those in your eyes, mouth, throat, and digestive tract.

The blisters on your skin usually form quickly and can be quite painful. But they’re not otherwise problematic. In severe cases, the cantharidin can make it through the fatty layer of your skin and cause body-wide symptoms like: 

If you happen to rub some of the fluid in your eyes, symptoms can include: 

  • Pain
  • Tearing
  • Decreased vision
  • Damage to your cornea

If you somehow managed to swallow powdered blister beetles — or other cantharidin products — the results can be fatal. You could go into shock or end up with severe kidney damage. Other symptoms from swallowing blister beetles include: 

Animals can also develop severe symptoms from eating blister beetles. For example, there are reported cases of horses dying from eating too many of the beetles trapped in their alfalfa hay.

You only need to seek medical attention in severe cases of blister beetle exposure. This includes when it gets in your eyes and when it’s swallowed. If you or your pet has swallowed blister beetles or products made with them, you need to call poison control as soon as possible. Their number is 1-800-222-1222. 

If you get cantharidin in your eye, you may need to see an eye doctor for an evaluation and the best treatment recommendations.

Otherwise, the blisters aren’t a serious medical issue and should clear up on their own within a few days. To help the healing process, you should gently rinse the affected area and apply corticosteroid creams to help with symptoms. Your doctor may prescribe antibiotics to prevent skin infections from any open wounds.

If you have a local infestation in your garden, your safest removal strategy is to simply pick them off by hand. You can wear gardening gloves if you’re concerned about getting blisters. 

Commercial farms may need to rely on pesticides to manage a blister beetle infestation. In this case, the pesticides need to be chosen on a case-by-case basis and sprayed by a licensed applicator. 

For the individual household, blister beetles are only problematic when you accidentally squish them against your skin. As long as you never ingest them, they’re a manageable pest. Industrial infestations will require more creative pest management solutions.