Watch for Blister Beetle in your Alfalfa! - This bale had 50 to 60 beetles visible between several of the middle flakes of the hay. Certainly enough to kill a 1200# horse, to say nothing of a Mini. In picking through the hay for a count, I actually ended up with little blisters on my fingers and hands. Imagine what a tongue or mouth would feel like let alone an esophagus, stomach, or intestine! - Jan Gauntlett, Mars-Montrose Miniature Horses & Llamas

Typically, adult blister beetles emerge from the soil during mid-to late summer. This insect group becomes a problem when beetles are killed by modern harvesting equipment and incorporated into baled alfalfa. Dead or living blister beetles contain cantharidin, an irritant of the gastrointestinal and urinary tracts of horses. Typical symptoms of cantharidin poisoning of horses include abnormal breathing patterns, the horse standing with its mouth in water for long periods of time and general restless behavior. Also mentioned in another article was these symptoms, ulcerations of the mouth, frequent play in water with lips and tongue, pawing, frequent attempts to urinate, stretching, jerking contractions of the diaphragm, diarrhea, discared intestinal tract lining in the stool and reduced levels of calcium and magnesium in the blood. If blister beetles are consumed by a horse, a vet. should be called immediately. Researchers believe that as few as 50 to 100 beetles consumed in a 24 hour period can result in poisoning and possible death of a horse. Another article says that 30 to 50 striped blister beetles would need to be eaten in order to kill a normal sized healthy horse. As few as two to five may cause colic in horses.