Blister Beetles in Hay

A very sad story and a precaution!


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I have lived in Arizona my entire life and had horses, but did not know about the devastating effect of Blister Beetles (Epicauta sp.) until very recently.

A touching story by a lady  in SE AZ has made it so the Blister Beetle will be much more prominent in my mind. She lives down in South Eastern Arizona and the Blister Beetles are endemic to that area of Arizona. In Phoenix and in Yuma,  the head and dryness tend to keep the Blister Beetles away. But, I have now heard of Blister Beetles in Pomerene, McNeal, Elfrida, Sunsites....all in Arizona.

Swarms of blister beetles commonly congregate around hay fields to feed on pollen and plant nectar and to mate. If the hay is cut while they are present, they can end up inside of a horse. Even if the hay is crimped and you can't see the bodies of the beetles, the endotoxin is there. The blister beetles contain an endotoxin, cantharidin, which is thought to protect the insects from their natural predators. Cantharidin is a terpenoid compound that is a strong vesicant that is extremely irritating to skin and mucous membranes and is rapidly absorbed and eliminated in the urine. It blisters a horses' entire intestinal tract (oral and gastrointestinal mucous membranes, urinary tract, and other organs), the gut shuts down and they go into renal failure. Even with infusion of liquids by IV, the gut dies, and the horse may die with it.

Clinical signs  may vary depending on  the severity of poisoning but may include: colic, sweating,  refusal to eat, salivation, congested oral mucous membranes, ulceration of the oral mucosa, washing the muzzle in water, straining to urinate, blood in the urine, elevated body temperature, diarrhea, abnormal heart rate and respiration, fever, and muscle stiffness with short-strided or “goose-stepping” gait.

The lady in SE AZ sent an email telling about the terrible losses she endured. I asked her if I could post her email to help others be aware and she has given me permission.  If you suspect your horse has eaten Blister Beetle hay, get veterinary care immediately. Here is a summary of her story:

Two of my horses have died since I fed them hay from a new bale last Wednesday evening. The vet bills total over $3000 and the efforts we made round the clock infusing them with IV fluids to try to flush the toxins out of them and get the guts moving again failed. Upon examination of the hay by  a veterinarian yesterday, over 30 blister beetles were found in one flake of the hay that I had fed to my horses Wednesday evening. My beautiful sweet three year old filly died by 5 pm Friday evening, my bred 12 yr old mare, a beloved mare sired by my old stallion that died in 2005, died this morning at 4 am. My friend also borrowed a bale of hay from me and fed it to her horses. A 6 year old gelding is sick and I don't think he is going to make it as he has not pooped in several days. My yearling filly has a depressed appetite and is not drinking much, she may be next. Three other foals and two other mares seem to be ok, but we won't know for a week or so yet if they are alright.
I did not buy this hay because it was cheap. I paid as much or more for it than I could have bought hay for in a feed store. I bought it because it was beautiful hay, mixed orchard grass, oat grass, Bermuda grass and alfalfa.
Cattle are not affected by them, because the rumen breaks everything in it down before the material goes into the gut. But the beetles are deadly to horses, and for that matter, people, dogs, anything that does not have a rumen. The blister beetles are endemic to this area and all it takes is one flake of hay that the beetles are in to kill or severely sicken your horse. Most horses do not survive. Mine didn't despite our efforts to save them, and I think at least one more will die, and maybe my yearling filly, too.

Several "old timers" here have now told me that they are a wet season insect, and come with the monsoons, and that one of the management practices that should be followed is to use only 1st & 2nd cutting alfalfa from this area, and none baled after the monsoons come, because that is when the beetles are likely to be in the hay. After I learned that my husband reminded me that the day the hay was delivered, it poured. You can see the beetles got caught in crimped hay, which is exactly the what will lead to the beetles being in the hay and not being able to escape before it is baled.


It was bad enough to loose the two wonderful mares, but then the rest of mine were sick, too. They apparently didn't get enough to kill them, but they were lethargic, off their feed, mouthing, and picking at the ground looking for little scraps to eat even though there was hay in their feeders. The mares that died did the mouthing, too, and we figured out that it was because their mouths and throats were so sore. The picking at the ground for little scraps was because the small pieces they could find could be swallowed without much chewing and went down easier than larger pieces of hay. They were not sweating and trembling like the mares that died, but they were sick, and a horse that isn't eating is a horse that will die because the gut won't be moving. I was sitting crying looking at them Sunday morning, a few hours after we buried the second mare that had died at 4 am, sure that the rest would follow and not knowing what to do. I was so exhausted mentally and physically by that time that I couldn't even think. The Veterinarian called me and I told her of my fears. She said, give them Banamine to make them comfortable, give them wet bran mash with carrots and apple bits and molasses and a bit of grain in it to get them to eat it, water the hay, water their feed, squirt a bottle of Maalox down their their throats, mix 1 qt mineral oil and 1 qt water and electrolytes together and squirt it down their throats with a turkey baster, squirt water down their throats with the turkey baster, and put a garden hose in their mouth at very low pressure and try to get them to swallow. I sprang into action, and actually all it took for mine was the Banamine and bran mash. They were hungry, their mouths and throats were just too sore to eat hay. They just inhaled the bran mash, and by the time they were done eating it, the Banamine had kicked in and they tore into the hay. I had in the meantime gotten some timothy hay, which is what I usually feed. It is so much softer and more palatable than the Bermuda that I had gotten to tide me over until I could get more timothy, they just inhaled that. They are still on Banamine, at half dose now, and a bit of bran mash, but they are eating and drinking and best of all pooping normally now, so they are going to be ok.

My girlfriend borrowed a bale of hay from me, and fed it mostly to one QH gelding. He is still pretty punky looking, we thought we lost him two nights ago, but yesterday morning he was standing with the other horses. So we put him on Banamine, and she got Maalox and mineral oil/water/electrolytes down him twice or maybe three times yesterday. Her husband has been trailering him around the neighborhood to keep his guts rattled up and moving, and he is pooping some, not as much as we'd like, but he has gut sounds and he is eating and drinking. He hasn't given up, so we haven't given up on him either. I am cautiously optimistic that he will pull through.




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