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Blister Beetle – How To Control Blister Beetles [In The Garden]

The blister beetle – there are more than 2500 different species and types of blister beetles (scientific name Meloidae) worldwide, so no matter where you live you are sure to encounter them at some point.

In the United States alone there are over 250 different kinds.

You will find blister beetles in grassy areas, croplands, and gardens in all parts of the nation. It’s also included in our “Bad Bug” article – Bad Garden Insects: A Guide To Identifying Garden Pests (30) To Control

Blister Beetle

Blister Beetle image via Flickr

They also live in desert settings. In this article, we will share information on blister beetles and the threats they pose to crops, gardens, livestock and people.

We will also provide tips and advice on avoiding them and keeping them under control. Read on to learn more.


What Do Blister Beetles Look Like?

There are hundreds of types of blister beetles worldwide, so their appearance differs quite a bit from one place to another.

Generally speaking, their bodies are long, soft and cylindrical. They are typically between a half-inch and an inch long.

The blister bug has long, thin necks and their heads are quite large with very long antennae (approximately a third the length of the body).

Blister bugs are long-legged, with soft, flexible wings. They can fly and travel in large swarms.

Brightly colored and variegated, the markings and coloration of blister beetles vary greatly from one type to another.

They may be solid gray or black, shiny bluish-black or greenish-black. Some are striped in shades of brown, gray and yellow.

Margined blister beetles are black with gray or cream-colored trim on the margins of the wing covers.

This illustrated list shows blister beetles commonly found in Florida, but these can also be found in other parts of the US. [source]


The Life Cycle Of The Blister Beetle

The adults lay eggs beginning in mid-spring and continuing throughout the summer months. Females lay eggs just below the surface of the soil.

They can lay as many as two-hundred eggs in a space measuring as little as 1mm x 2mm. It takes a couple of weeks (or less) for the eggs to hatch.

When the white larvae emerge, they have fairly long legs and they set about seeking grasshopper eggs, which they eat.

At first, they eat voraciously; however, as they move through the 4-7 stages (instars) necessary to mature, they feed less. As the larvae mature, they become darker in color.

After only ten days, they will have transformed from soft, white, long-legged larvae to pupae to fully formed adults.

Late hatching larvae overwinter underground as semi-pupae. In the springtime, they emerge and molt.

In the summertime, they mature into adult beetles, which usually live about three months. The females lay clusters of eggs multiple times during their short lifespan. [source]


Adult Blister Beetles’ Diet And The Damage They Do

Adult beetles eat all kinds of leaves. You can find them on grasses, but they especially love legumes and are a real problem in alfalfa fields.

In your home garden, you will find them on all sorts of leafy greens as well as:

…and many other types of vegetables.

They also eat flowers and leaves of most types of plants. They tend to travel in swarms and will descend on a garden suddenly and strip it bare quickly.

black blister beetle feeding on flower

Black Blister Beetle dining on red flower


Blister Beetles Do A Lot Of Damage To Crops

When large numbers of blister beetles swarm they can do major damage to commercial crops.

They are especially threatening to tomato, potato, beet and alfalfa crops.

When a swarm descends on alfalfa fields for example, it can completely strip it in a matter of hours. [source]


Blister Beetles Pose A Risk To Livestock

Blister beetles use an irritating chemical called cantharidin as a natural defense.

In the wild, this chemical does little harm to potential blister beetle predators.

When a bird or other animal interferes with a blister beetle, the bug’s joints exude cantharidin in an action called “reflex bleeding.”

When the would-be predator comes in contact with this chemical, it lets the bug loose and both go their merry way.

When blister beetles get crushed up into hay, it’s a different story. The crushing causes the cantharidin to ooze out into the surrounding hay where it stays potent for many months.

When livestock eats this hay, it causes severe burning.

Horses, cattle and other livestock that eat hay containing dead blister beetles can be severely poisoned and may even die.

The toxin causes severe irritation of the mouth, throat and digestive system. Blistering of these sensitive tissues can be rapid and severe.

If a great deal of the toxin is ingested, it can cause kidney and/or liver failure.

A few blister beetles in hay may be irritating to livestock. It takes a lot of beetles to do serious damage and become a lethal dose..

Generally speaking, ingesting cantharidin from around one-hundred beetles could kill an 800-pound cow, horse or other animals.

While this may seem like an awful lot of beetles, remember that these bugs tend to travel in swarms and congregate in groups, so ingesting that many over the course of a few days would not be impossible. [source]

Take Care When Growing, Harvesting Or Purchasing Hay

The types of blister beetles most commonly found in hay bales are the black, spotted and three-striped varieties.

Of these, the 3-striped blister beetle has the most potent poison.

If you are growing grass or alfalfa for hay, inspect your crop regularly for beetles.

When you cut your hay, don’t use a hay crimper because it will crush the bugs and release their toxins.

Once your hay is cut, let it dry in the fields for at least two days so that the live beetles can move on before you bale.

When purchasing hay, look for first cuttings because early hay is less likely to contain blister beetles than later cuttings.

It’s always a good idea to buy your hay from a reputable grower who takes hay production seriously.

Growers who depend on a good reputation are sure to examine their crops frequently and take appropriate steps to deal with blister beetle infestation.


What About Blisters On People?

Blister beetles don’t sting or bite, but they can have a toxic effect.

When these bugs bungle into people, they often get crushed on the skin.

When blister beetles are crushed, they exude a great deal of hemolymph (bug blood) in a process known as reflexive bleeding.

This red goo contains an irritant called cantharidin. When this blistering agent substance comes in contact with human skin, it can create some very dramatic looking and painful blisters.

This typically happens at night when blister beetles are attracted to outdoor lighting and accidentally come in contact with people.

Cantharidin can cause blistering on the skin on contact, but this is not usually serious and will resolve on its own.

If ingested, this chemical can cause severe gastric distress or even death.

If cantharidin absorbed in large amounts through the skin, it can be very toxic to humans and other mammals.


How To Avoid And Treat A Blister Beetle Bites

If a beetle lands on you, don’t crush it.

Even though these bugs are very big and creepy, try to keep your wits about you and just brush the bug off with a napkin or some other item to protect your hand.

If the bug has landed on your bare skin, wash as soon as you can. Remove any clothing the bug has landed on and wash it.

Light brushing is unlikely to trigger reflexive bleeding.

Blistering is most likely to occur on very thin skin (i.e. the skin between your fingers, inside your wrists, on the back of your neck, etc.)

If this happens, take care of it as you would any burn or blister.

Unless it covers a large area, you probably do not need medical attention. Just use standard first aid techniques to clean and protect the area.

A cool compress can help resolve any burning sensation.

You usually will not encounter blister beetles unless you are working in your garden or out in nature.

To avoid contact with cantharidin it’s wise to wear long pants and long sleeves when you are in areas where blister beetles may be present.

If you do encounter a blister beetle, avoid touching it. If it lands on you, remove it gently.

Most of the time, exposure to blister beetles is not life-threatening or even especially bothersome.

Just be sure to wash your hands after brushing beetles aside because you don’t want to get even the smallest amount of toxin near your eyes.

Getting cantharidin into your eye can lead to serious consequences. If this happens, you should seek medical assistance.


Why Do Blister Beetles Make Cantharidin?

We naturally assume that it is intended to dissuade predators, and there is some evidence of that.

Biologists have found that the substance is also conveyed from the male beetle to the female in great quantities during mating.

Furthermore, the female coats her eggs with the substance after laying them.

This probably helps protect the eggs from being eaten by predatory insects.


Blister Beetle Control – What Can You Do

Vigilance always pays off in gardening. You may begin to see a few early in the summer, then suddenly a swarm of them may appear.

You will see them in big bunches on your lettuce, potatoes, and other leafy green veggies.

Stay familiar with your garden patch by inspecting every day. As soon as you see a blister beetle, begin taking action.

Hand picking is a good way to control them as long as you wear rubber gloves to protect yourself.

Because they tend to congregate in groups, you can just knock them off plants into a bucket of hot, soapy water to kill them off.

Dispose of the hot water and the beetle carcasses carefully because both will contain the blistering chemical, cantharidin.

Remove as many as you can by hand, and also remove the damaged plants as there may be some scent element involved in attracting them to your garden.

Be sure to act quickly to prevent them becoming established.

Once they are entrenched, it’s hard to get rid of them – even if you spray them with poison.

Note that if you shake beetles off the plants onto the soil, they tend to lie still rather than running off.

This is a good time to sweep them up into a dustpan and dump them into a bucket of hot, soapy water.

To prevent them taking up residence in your yard and garden, keep your weeds low.

If there are thick, weedy verges around your garden, adult beetles will surely feel compelled to lay their eggs there so that the larvae can take advantage of grasshopper eggs in the soil.

Be sure to keep Amaranthus (pigweed), Ambrosia (ragweed) and Vernonia (ironweed) under control because these beetles just love it.

If you have it on your property (or if it is growing on neighboring properties) it will attract them.

Once they’ve decimated it, they’ll move on to your garden plants.

You can use non-toxic deterrents against these beetles.

For example, spreading diatomaceous earth on the ground around plants that will attract them can kill them off as they emerge from the ground after pupating.

You can also create a barrier using oyster shell lime.

This will not kill them, but it will discourage them (while helping condition your soil).

Late in the summer, you can prevent the adult beetles from moving row-to-row in your garden by setting up firmly anchored row covers.

This won’t stop larvae emerging early in the springtime, but if you also sprinkle diatomaceous earth around the covered plants, you should have the situation fairly well under control.

As for insecticides, Spinosad is a somewhat effective pesticide for use against blister beetles.

This pesticide must be ingested to work, and these beetles consume it when they consume greenery.

It will kill off most of these bugs within 48 hours, and it breaks down in the environment in two or three days, so it does not pose an ongoing threat to beneficial insects and other wildlife.

It is not toxic to fish or birds, but it is toxic to honeybees, so be sure to apply it at dusk so that it will have time to dry before bees are present.

Spinosad also helps keep your grasshopper population under control. This is a good thing since their presence will attract blister beetles.

If you have a grasshopper problem now, be advised you may very well have a blister beetle problem later.


Is There Anything Good About Blister Beetles?

Because they eat grasshopper eggs, the larvae can be considered somewhat beneficial; however, as adults, they are trouble through-and-through.

Desert-dwelling blister beetle larvae eat wasp larvae. The way this comes about is quite interesting.

Adult beetles can be rather dashing in appearance, and the blister beetle toxin, cantharidin, does have some medicinal uses. [source]

Cantharidin is an odorless terpene.

It is an irritant that is used in some topical medications, such as those meant to remove molluscum contagiosum, plantar warts, and other skin defects. The chemical is also sometimes employed in tattoo removal.

Cantharidin is also desirable to certain types of large birds.

According to National Geographic, male Great Bustards enjoy a “daredevil diet” of certain types of blister beetles during mating season.

During this time, the birds eat a measured number of blister beetles daily as a way of ridding themselves of parasites.

This makes them more attractive to the opposite sex. [source]


Handle Blister Beetles With Care

Blister beetles sound very scary, and they can be.

If you encounter them in your yard or garden, be sure to proceed with caution. Always wear rubber gloves when removing them from plants.

Understand that cloth gloves cannot protect you.

If you choose to use a pesticide to deal with them, remember to follow all packaging instructions closely.

Additionally, sweep up all the dead beetles and dispose of them in a sealed plastic bag to prevent any person or animal from coming in contact with them.

If you pay close attention and deal with blister beetles as they show up, you can probably prevent having an overwhelming infestation.

In this case, a little tolerance can go a long way.

Taking a live-and-let-live attitude toward a few of these pests can be safer and easier on your blood pressure levels than attempting to eradicate them completely.