Alfalfa farmers beware of destructive blister beetles, cause toxic contamination of hay

Farmers getting ready to cut alfalfa should keep a sharp eye out for blister beetles that can potentially cause toxic contamination of their hay.

Species vary in size and color, but are recognized by elongated, narrow, cylindrical, soft bodies. When viewed from above, blister beetles have an accentuated neck.

All species of blister beetles have only one generation per year. Adults are seen after they emerge from the soil and begin foraging. Egg clusters, with up to 100 eggs, are deposited in the ground during the summer. With in two weeks, tiny larvae hatch, eating primarily grasshopper egg pods. These larvae go through three more stages before they lose their legs and develop a thickened skin to overwinter and remain in this state for seven months. The final immature stage develops with favorable conditions in the late spring. Finally, after two weeks as a pupa the adults emerge, typically in June and July.

Large swarms of three-striped blister have been observed in west-central Kansas indicating peak summer activity for this species. This is one of the most common blister beetles in Kansas and is distributed throughout the state. Others include the spotted, clematis, and black.

Blister Beetles contain cantharidin which is a chemical irritant capable of blistering body tissues that are exposed to the chemical. Most frequently, livestock come into contact with these beetles when they consume alfalfa hay containing dead beetles.

Dense aggregations may occur in patches of the field and these should be allowed to disperse naturally before mowing. It is important to avoid driving over, mowing or crushing large aggregations prior to, or during haying.

Once hay is contaminated with cantharidin, the hay will not loose its toxicity as cantharidin is a stable compound, withstanding degradation by heating or drying. Therefore it is important to keep the beetles alive and healthy so the can remove themselves from the field.

There is no definite answer to the age old question, "How many does a horse have to eat?" The species and sex of the beetles, the size and health of the horse, and the amount of cantharidin ingested all influence the onset and rate of symptoms. Cattle are much less susceptible, but lab studies have shown the decrease of digestibility when present.

Contact with the chemical causes blisters and ulcerations to occur on body tissues. Colic and diarrhea may be noted along with blood and/or discarded intestinal linings. Lowered calcium levels may result in body tremors or breathing patterns characterized by periodic jerks of the diaphragm. Other complications may include congested mucal membranes, elevated temperature, pulse and breathing rates, and depression and shock.

With any suspicion of beetle infested hay being eaten, a veterinarian should be consulted.

Editor's Note: Delta George is a K-State Research and Extension agriculture and 4-H extension agent assigned to Bourbon County. She may be reached at (620) 223-3720.