Blister beetles plaque the alfalfa industry

What does a blister beetle look like?
Blister  beetles identification picture
Black blister beetle

Horse eating hay

blister beetles

blister beetle image 1

Flake of mechanical conditioned hay. Dead blister beetles in this hay are deadlier than live blister beetles

Blister Beetles

It is unfortunate but the blister beetle has plagued the alfalfa industry 

Know where your hay comes from

Buy from Hay USA Inc.

The people you can trust.

It's a wise investment.

Blister beetles are one-half to one inch. long and have soft bodies. The head is broad and vertical. The section of the body between the head and the wings (prothorax) is narrower than the wings, and narrower than the head. It appears that the insect has a neck. The wings are soft and flexible, and the legs are long. Striped blister beetles are about 5/8 inch long and one-fourth as wide. They are gray to brown with yellow stripes running lengthwise of the wing covers. The ash-gray blister beetle is about 1/2 inch long and is completely gray. The black blister is about 1/2 inch long and is solid black.

The larvae of the blister beetles destroys grasshopper egg pods. Infestations often occur during or just following a grasshopper outbreak. The black blister beetle adults are largely pollen feeders, but they also feed on alfalfa blossoms. Blister beetles have an oily substance, cantharidin, in their body fluid that causes large blisters to form when a beetle is crushed.

Blister beetles have a wide host range including alfalfa, clover, soybean, potato, tomato, melon, cotton, and eggplant.

Cantharidin was first isolated in 1810. It is odorless and colorless.

  • It is secreted by the male blister beetle and given to the female during mating. Afterwards the female beetle will cover its eggs with it as a defense against predators.
  • Horses are highly sensitive to cantharidin and it is often deadly.
  • For horses a lethal dose is approximately 1 mg/kg of the horse's body weight.
  • Horses may be accidentally poisoned when fed bales of Alfalfa with blister beetles in them.
  • Cantharidin is comparative to cyanide and strychnine in toxicity.
  • Cantharidin will remain toxic in dead beetles.
  • There is no sampling method that will detect Cantharidin in cured baled hay or cubed or pelleted hay.
  • Cantharidin can not be broken down by heat or mechanical devices.

Cantharidin can cause sever inflammation and the formation of blisters on the skin.  If absorbed through the intestines, symptoms can include inflammation, blisters in the mouth, straining, temperature, increased heart rate and respiration, sweating, diarrhea and frequent urination within the first 24 hours.
This is accompanied by secondary infection and bleeding.  Calcium levels in the horses may be drastically lowered and heart muscle tissues destroyed.  Animals can die within 24 to 72 hours, so it is imperative to contact a veterinarian as soon as a blister beetle poisoning is suspected.

Toxic to Livestock:
Cantharidin is toxic to livestock. Cantharidin is contained in the (blood) of the beetles and may contaminate forage directly when beetles are killed during harvest. Handling these insects may result in blisters, similar to a burn. Blister beetles have been a serious problem in alfalfa in the northern United States, the Midwest, and the south for many years. We have found West coast Alfalfa to be safest. We always recommend checking your alfalfa for extra security. Nothing is 100%. Your horse depends on you.

Beware Buyer:
There is beautiful hay through out this country and Canada and very reputable producers who take every precaution in regards the beetle epidemic.
Beware of mechanical conditioners. Mechanical conditioning crimps the hay to create a soft green texture by removing moisture within a matter of hours. Unfortunately this kills the Blister Beetles trapping them in the hay. A dead beetle is deadlier than a live beetle! Please don’t be taken by pretty hay, go for safe hay. Beware of a salesman that says that there are no Blister Beetles in their state. Blister Beetles are in every state in the United States. Educate yourself, check your hay before feeding. Your horse depends on you!

Don't be scared to feed alfalfa, learn about Blister Beetles. Hay USA has Safe hay!

Dare to compare!


Nation wide Call 817-599-0200
for current retail and full load prices.
Hay USA Inc. feeds a wide variety of horses.
We supply hay for top performing horses, breeding facilities large and small to the
back yard horse owner.
Our clients are educated and can not afford to take risks.
That is why they buy from Hay USA Inc.

Click here for client testimonials.

Hay USA Inc.
1714 Blair Drive
Weatherford, Texas 76086
Call nation wide 1-817-599-0200


Business Hours 10 - 6 Tuesday - Saturday