Among our common harmful insects we find the family of blister beetles. They are notable for the greater number of changes they undergo during their lifetime compared to the usual metamorphosis of most beetles. Blister beetles are soft-bodied, slender-legged, medium to large-sized insects with broad heads and a narrow thorax, and are generally slender in shape. They range in colors from gray, black, or brown to bright metallic shades of red, blue, green, or yellow. All of them feed on plants in the adult stage, their food consists of leaves, flower petals or pollen from various plant species. Our most common and destructive species in the East, belonging to the genus Epicauta, causes considerable damage in our gardens.
A yellow and black striped form is known as the “old-fashioned potato beetle”. The “marginated blister beetle” has also been known to attack potatoes and completely defoliate the plants in certain areas. They also feed on the foliage of beets, tomatoes, and especially clematis. This species is greyish-black, always margined with gray wing coverts. It is about five-eighths of an inch long. One of our most common species is the black blister beetle which occurs very commonly on goldenrod, but all this has nothing to do with the name “blister beetle” given to it because of its peculiar physiological properties. A substance called “cantharidin” is found to a greater or lesser extent in the body of almost all members of the family. This substance when applied to the skin causes an inflammatory or blistering effect. To take advantage of this property, the beetles are dried and pulverized, and the powder thus obtained is used in medicine. Beetles commonly used for this purpose come from Spain and other European countries, and are known as “Spanish fly”. Returning to the remarkable life history, we find that adult females lay large numbers of eggs in the soil or on plants, depending on the species of blister beetle in question.
These eggs hatch into very long-legged larvae that run around in search of food. Some of these active young find the grasshopper eggs on which they feed. However, according to statistics, even this habit is of questionable value, since they also destroy other, more valuable parasites from grasshopper eggs. Other species of these slender-legged blister beetle larvae find a situation where they observe bees. When the right one appears, they attach themselves to the furry body, and the unsuspecting bee carries them home to its nest. Here, the young blister beetle after stealing the ride, settles into the bee’s nest and proceeds to devour the bee eggs and larvae, and eventually the accumulated provisions that were provided to the young bees. During this time, the blister beetle has completed its own complicated life cycle, fully transformed, and an adult beetle will emerge in place of the bee.