During the past two weeks, several bulging blister beetles appeared in my lawn. While their rotund abdomens and striking color provide a comical appearance, these insects should not to be taken lightly. If handled roughly or crushed against your skin, blister beetles release blood laced with potent irritants called cantharidins. These compounds raise nasty looking blisters upon contacting skin. Blister beetles occupying plants in meadows may be inadvertently bailed in hay and fed to horses and other farm animals. The toxic cantharidins in their bodies can be lethal. Blister beetles are also the source of the medicinal compound called Spanish fly. The term Spanish fly refers to a particularly beautiful European species of blister beetle, Lytta vesicatoria from which cantharidins are extracted. Much lore surrounds cantharidins as potions of love, healing, and death. Love potions concocted with Spanish fly are said to be potent aphrodisiacs. One remarkable tale I stumbled across described a gathering hosted by the infamous Marquise de Sad. To liven things up a bit, the Marquise slipped the guests a little Spanish fly on some sweets. Unfortunately, he miscalculated the effective dose and rather than arousing his guests several were poisoned and died.
Spanish fly was also used as a medicinal in America’s revolutionary era. The father of our nation, George Washington, had a most disagreeable encounter with Spanish fly. After taking ill, President Washington was near death on December 14, 1799. As was common medical practice at the time, Spanish fly was applied to his neck in an attempt to draw out the inflammation. The Spanish fly therapy and several bloodlettings on the same day proved a bit too much for our ailing founding father and he expired. Other than packing a nasty wallop of poisons adult blister beetles live rather placid lives munching leaves or eating pollen.
The larvae of blister beetles are another matter. They are enemies of other insects including solitary bees such as plasterer bees we met in previous episodes. A sunny backyard hillside sparsely cloaked in grass, has become the residence for a large colony of plasterer bees at my home. This spring I captured a dozen large female blister beetles carefully patrolling the soil in search of bee burrows in the earth. I watched one beetle with a particularly bulbous abdomen spend more than half an hour scooping soil from the bee’s burrow to enlarge the entrance. When the hole was suitably magnificent, the beetle hit a 180 and wedged her enormous rear-end into the earth. Although I cannot verify the next event, I am reasonably certain that she deposited her load of eggs into the gallery of the bee. When her task was complete, she carefully sealed the hole with soil and departed. After hatching from eggs deposited in the ground, tiny blister beetles larvae called triungulins get busy finding food. In some species triungulins descend into the gallery of the bee and consume the pollen cakes prepared by the mother bee for her young. After the provisions are consumed the blister beetle larva eats the baby bees - quite tragic really. Larvae of other species of blister beetles scurry on the ground and locate nests of grasshopper eggs. Hungry triungulans burrow into the soil and the underground omelet becomes a banquet for the blister beetle larvae. If you see blister beetles on plants near your home or in the meadow this spring, resist the urge to handle or eat them unless you desire a blistering surprise.
The wonderful reference “Insects: Their Natural History and Diversity” by S.A. Marshall was used to prepare this episode. To learn more about blister beetles and their lore, please visit the following web sites.