The Blister Beetle

A blister beetle has made its appearance in this area, and probably elsewhere. This one is in the genus Epicauta, one that is feared by hay producers and livestock owners alike for its poisonous properties. These beetles are also about half an inch long, more or less with cylindrical, thin bodies. Their wing covers are fairly soft and are easily compressed when they are handled, even gently. They are a rather dull bluish gray, peppered in tiny black spots. Their black appendages never seem to rest when the beetles are alive; they always seem to be frantically crawling somewhere, beating their threadlike antennae. Adults are fairly strong fliers and tend to be gregarious. They fly around in large groups ("swarms") in pursuit of good plant-type food. When they land in alfalfa fields, they are no doubt cooled and refreshed by the crop but it is the flower buds and blossoms that they seek. Alfalfa growers usually time their cuttings to coincide with early bloom of the field. When hay swathers cut and windrow the fragrant plants, they harvest the beetles, too, unfortunately. The more modern equipment spindles the cut plants slightly to speed drying so that bales can be made and shipped promptly. Unfortunately, this spindling mashes whatever insects might be on the alfalfa at cutting time.

So what? Blister beetles get their common name from their tendency to cause blistering of skin (and other tissues) that may contact either the beetles or their internal contents. If these beetles are picked up with fingers or forceps, note that they will often bleed at the leg joints; alternatively, they will regurgitate. Either of these fluids contain "cantharadin," a potent blistering agent made by the beetles; while it may be a by-product of beetle digestion, cantharadin may chemically protect these beetles from their natural enemies. When accidentally streaked on tender skin—on the insides of the arms, practically anywhere on the face, neck, chest or legs—the skin erupts in painful "water blisters." If these are broken-accidentally or on purpose-the resulting fluid can even blister again, wherever it is streaked over adjacent skin. This happens on human skin but the results involving livestock, particularly horses and their relatives, are considerably more damaging. The cantharadin will blister the inside of the animal’s mouth, tongue and esophagus, leaving the animal in considerable pain. Not only are they "off feed," but also they can be found plunging their muzzles into their water troughs. The cantharadin persists in the animal’s system, next attacking the bladder and kidneys, causing hemorrhage. It may also inflame the pericardial sac around the heart. Affected animals die in extreme misery and often within a few hours or days of poisoning. While results like this are pronounced in horses, they can also occur in cattle. The beetle does not have to be intact or even recognizable to cause poisoning; just the body fluids—even dried body fluids—can poison livestock.

Alfalfa growers in particular are reminded to SCOUT, SCOUT, SCOUT their fields well in advance of each harvest; if done early enough, there are appropriately labeled insecticides for these pests that can be used safely just prior to harvest, permitting the beetles to drop off the plants before cutting and baling.