Alfalfa is one of the best hays for horses, but it also may house one of the
animal's worst enemies. It takes relatively few blister beetles to kill a
horse -or a cow or sheep. "When you're selecting hay for horses talk to the
supplier, not the hay broker, to find out when and how it was cut and
whether scouts were looking for blister beetles," says Texas Extension horse
specialist Pete Gibbs.

Midsummer alfalfa is more likely to contain dead blister beetles that
first-cutting hay or late cuttings. The process of cutting and crimping at
the same time traps and kills the pests in the hay. Dead beetles appear to
be the problem, because live ones can escape before the hay is baled.
Blister beetles are attracted to the blooms, so the best time to cut alfalfa
hay is in the bud stage and when there are no flowering weeds.

Theses pests contain cantharidin, which is highly toxic to horses. The male
beetles manufacture and transfer it to females while mating. It's the same
stuff that raises a welt when one of these beetles lands on your bare skin,
which is how the pest got its name.

There are several kinds of blister beetles, some containing more cantharidin
than others. Each type has a different coloration. Many common beetles
have long, narrow bodies (3/4 to 1 1/4 inches), broad heads and antennae.
Unlike most beetles, their front wings are soft and flexible.

Nebraska specialists note that just a few blister beetles with a high
cantharidin level could kill a small horse. For instance, striped blister
beetles contain a higher level of poison than black ones. So it would take
1,700 black beetles to kill an 825-pund horse, but the ingestion of a mere
120 stripped ones would prove fatal to the same animal. And a 275-pound
horse could be killed by as few as 25 striped blister beetles. It would not
be unusual for a horse to consume a large number of beetles, because the
insects tend to feed together on blooms and might all be killed and
preserved in the same bale of hay.

Call a vet as soon as you suspect blister beetles poisoning. 
There's no antidote, but your vet may be able to decontaminate the horse's digestive system.

-Karl Wolfshohl
Progressive Farmer/August 2003,pp 22

Act quickly
The following symptoms may help you recognize blister beetle poisoning in your animal:

- Diarrhea and frequent urination in the first 24 hours.
- Blisters and ulcers in the mouth.
- Colic, straining, fever and sweating.
- Increased heart rate and rapid breathing.

It's important to pay attention to these symptoms, because this condition
can result in death. Cantharidin destroys heart muscle, 
killing the animal within 72 hours.

We have noticed there are un-licensed and un-trained persons spraying herbicide on horse pastures in our area. In accordance with the Department of Agriculture rules, all persons spraying for a fee must be licensed by the Department of Agriculture. These herbicides can be dangerous when used improperly. It is your horse, your responsibility, and your right to know if the person spraying herbicide on your pasture is a licensed pesticide
contractor.