Blister Beetle

The blister beetle, also known as an oil beetle, is a family of plant-eating insects which have the ability to excrete a toxic substance from their joints when feeling threatened.

This fluid, called cantharidin, can cause painful swelling, irritation, and blistering on the human skin. These symptoms disappear after several days, especially with the application of dermatitis treatment, and rarely leave behind any long-term effects.

Nevertheless, blister beetles actually cause quite a lot of damage to crops and plants. They also pose a more serious threat to livestock such as horses, cattle, and sheep, which may accidentally ingest large quantities of cantharidin if it’s ground up in hay. The toxin, which persists long after the death of the beetle, may cause irritation and inflammation of the digestive and urinary tract, and depending on how much is ingested, there is the possibility of death after about 72 hours. For these reasons, it is considered to be more of an agricultural or livestock pest rather than an indoor pest.

4 Incredible Blister Beetle Facts!

• In many species, like the red-headed blister beetle of Arizona, the male beetle will remain attached to his mate for more than 24 hours in order to breed together. The female continues to move between flowers to feed as she carries him around.
• After mating, the female beetle will bury perhaps hundreds of eggs in the ground and let them hatch on their own. She does not provide any parental care, but she may coat the eggs with a bit of her own toxin for additional safety. Once they hatch, the blister beetle has a complex life cycle. It undergoes several larval stages, sometimes up to six or seven, in the winter. They become pupa in the spring and emerge as adults in the early summer. Most species leave behind only a single generation per year.
• The larva of the blister beetle is sometimes described as parasitoid, because it takes a living host to feed upon until it has enough energy to reach the next stage of its life cycle. Unlike a true parasite, however, this always results in the death of the host. The larva is quite mobile after hatching, which enables it to find a suitable host. It becomes less mobile as it settles down and matures, but the adult becomes highly mobile again in order to travel between flowers.
• The toxic cantharidin secreted by the beetle has been traditionally used by many cultures as an ointment (for gout or arthritis), an aphrodisiac, or a wart remover. This treatment is sometimes called Spanish fly, because the toxin is derived from the species of the same name.

Species, Types, and Scientific Name

The family name of the blister beetle is Meloidae. It’s not exactly clear what this name refers to, but it was thought to be first named in 1810 by the Swedish entomologist Leonard Gyllenhaal (who, interestingly, was an ancestor of the actors Jake and Maggie Gyllenhaal). There are some 7,500 recognized species worldwide spread across dozens of different genera. Well-known members of this family include the red-headed master beetle of Arizona, the black blister beetle of North America, and the three-striped blister beetle, also from North America. Most species don’t have a name beyond the scientific name; they’re poorly understood and under-studied.

Appearance: How to Identify Blister Beetles

The blister beetle varies quite a bit in size and shape, but most species are characterized by a wide head, a narrow thorax (the midsection), and a very long, cylindrical, or ball-like abdomen. They have two pairs of soft wings, in stark contrast to the hard front wings of most beetles. The blister beetle announces its toxicity with a colorful flourish. Against a black or gray base, many of their bodies have bright red, green, or yellow markings to signify their danger to potential predators. The red-headed master blister beetle of Arizona is one of the largest species, measuring more than an inch long. Most of them are not much larger than a coin.

Habitat: Where to Find Blister Beetles

The blister beetle is found in almost any warm or temperate habitat in the world with a sufficient amount of flowering plants to feed on.

Diet:

The blister beetle is generally omnivorous. It feeds on both insects and plant matter during its lifetime.

What eats the blister beetle?

The blister beetle is preyed upon by a large number of different mammals, birds, reptiles, and frogs. However, the painful toxin is a potent deterrent for any would-be predator that hasn’t evolved any protection against it.

What does the blister beetle eat?

The feeding habits of the blister beetle change throughout its life cycle. As a larva, the beetle feeds on immature bees or grasshopper eggs, sometimes following an adult back to their nest. As an adult, the beetle feeds on the flowers, nectar, and leaves of plants. Their most common targets include ornamental and vegetable crops.

Prevention:

Blister beetles do not pose much of a problem for most people, but they can sometimes make themselves a nuisance for farmers and gardeners by damaging crops and plants. Farmers should look for signs of blister beetle activity frequently throughout the harvesting season. Once they’re well-established, the blister beetles are hard to remove. Fortunately, they will usually gather together in large clusters out near the edge of the field, making them easier to spot. They are particularly attracted to alfalfa plants and weeds, although they also feed on tomatoes, potatoes, peppers, eggplants, and other vegetables.

As long as you’re only dealing with a small garden, the best strategy to control their numbers is to pick up the blister beetles by hand (with gloves on for protection) and place them into a small container. Large-scale infestations are much more difficult to control and may necessitate the use of chemical pesticides. Another solution is to change the timing of the harvest before the flowering attracts the beetles to the field. If they somehow end up lodged in the hay, then there are a few potential solutions. Swathing hay without crimping usually allows them to escape the hay without any damage. Raking the hay will also remove some of the blister beetles.