| Alfalfa hay can contain a potentially deadly bug called blister beetles. Although they
only cause limited damage to the plants, they can cause illness and even death if eaten by
livestock.
What are they?
Blister beetles are generally 1/2 to one inch in length and can be black, gray, brown
or orange-striped. They have a narrow, cylindrical body with a distinct neck. Blister
beetles contain a highly toxic drug called cantharidin that is very stable. Dried remains
of beetles in hay are toxic and, even after the dried remains are removed, the toxin will
often remain in the hay.
The beetles are found throughout the US, but are most common in the arid, western
states. They are also found in some eastern states, especially in years following heavy
grasshopper infestations.
There is usually only one generation per year. The females lay eggs in the soil during
late summer or early fall and the larvae hatch in about two weeks. These larvae then feed
on grasshopper eggs, overwinter in the soil, pupate the following spring and emerge as
adults sometime between June and August of the next year.
Blister beetles are attracted to flowering vegetation and frequently feed on foliage,
pollen and nectar of alfalfa, soybean and weed plants. They usually congregate in large
numbers in small areas of the field, usually within 50 yards of the edge. Because they
swarm and feed in large numbers, a small amount of hay can have large doses of the toxin.
What effects do they have on livestock?
Horses are most susceptible to the toxin and can die after ingesting about 1 mg of
cantharidin per kg (2.2 pounds) of horse body weight. Because a striped blister beetle
contains about 5 mg on average, it could take less than 100 of these small beetles to kill
a horse. In some cases as few as 30 to 50 can kill. As few as two to five beetles can
cause colic. Even hay that has dried juice from crushed beetles can cause symptoms.
The toxin causes irritation or damage to the stomach lining, small intestine, kidney,
urinary tract and urethra. The most commonly visible symptoms include ulcerations of the
mouth and frequent play in water with the lips and tongue. The horse will sometimes blow
into the water to relieve the stinging. Other symptoms include colic, shock, pawing,
depression, sweating, fever, frequent attempts to urinate, stretching, jerking
contractions of the diaphragm, diarrhea, changes in the gait, elevated heart and
respiration rates, dehydration, and reduced levels of calcium and magnesium in the blood.
Any horse showing these symptoms should be seen by veterinarian immediately. A horse
that has ingested large numbers of blister beetles can die within six hours. Although
there is no known antidote, treatment includes removing the source of the toxin (inspect
the hay for the presence of blister beetles), reducing absorption of toxin, protecting
digestive tract mucosa, controlling pain, and maintaining fluid and electrolyte balance.
Early detection and treatment can improve the prognosis.
Other animals, such as cattle and sheep may stop eating or may become sick after
consuming a large number of blister beetles.
What can you do to prevent problems?
If you are a horse owner:
Feed only first-cutting alfalfa for horses. Blister beetles don't usually emerge
until after the first cutting. Late fall cutting is also generally free of blister beetles
because insect activity usually ceases in early fall, however changing weather patterns
(particularly El Nino years) may affect when blister beetles are active in alfalfa fields.
Buy your alfalfa hay from known producers and ask about their harvesting
methods.
Check your hay for blister beetles when you feed. Blister beetles retain their
body shape and size even after death. Be sure to discard any hay that contains blister
beetles as the toxin could have contaminated the surrounding hay.
Although these tips can reduce the chance of blister beetle poisoning, it does
not eliminate the possibility.
If you are a hay producer:
Control weeds and adjust your harvest date. Blister beetles are attracted to
weeds and alfalfa in the flowering stage, so harvesting before bloom means fewer beetles.
Avoid using hay conditioners or crimpers that kill blister beetles during hay
cutting and trap their bodies in the hay. Live beetles will usually leave the area shortly
after cutting.
Avoid driving over cut hay which crushes the beetles in the hay rather than
allowing them to escape.
Apply an insecticide prior to harvest. Check the field about eight or nine days
before harvest to search for blister beetles, then use an approved insecticide such as
carbaryl (Sevin) or methoxychlor. Wait at least seven days after applying insecticide
before harvesting. Parathion is also effective, but has a 15-day waiting period before
harvest. Check your fields one or two days before harvest to ensure that your fields have
not been reinfested.
For more information and photos that can help you identify blister beetles, please see
the OSU Extension
Facts No. 2072. You will need Adobe Acrobat Reader to access this file.
The information given here is to help you learn more about your horse
and not to replace your veterinarian's advice. |
