By some unusual circumstance, Bug of the Week found itself in the Great Basin desert last week where we encountered some unorthodox beetles. These large and very juicy looking beetles appeared at dusk and wandered about the dessert floor feeding on vegetation with impunity. These giants were close to an inch in length and even in twilight, their jet-black color made them highly conspicuous against the light red earth of the desert floor. With hungry predators such as lizards, birds, and rodents, roaming about, the desert is a dangerous place for large, juicy insects. As I crouched to photograph the beetle, it halted and like some contortionist from Circe du Soleil, the bugger proceeded to stand on its head and lift both pair of hind legs off the ground. What manner of trick was this?
As I examined the creature a bit more closely with my fingers, my reward was the distinct unpleasant odor of organic compounds discharged from the rear end of the bold beetle. Later my fingers turned a curious shade of brown where the quinones squirted by the beetle reacted with the air and my skin. This marvelous denizen of the desert was a darkling beetle in the genusEleodes. Eleodes has evolved an elegant defense against other animals that would like to make it dinner. Dr. Thomas Eisner discovered that within the abdomen of Eleodes two large glands produce several types of quinones and other organic compounds. These noxious chemicals are very irritating to mucus membranes such as those lining the mouth and eyes of predators like birds and toads. Quinones are also repellent to hard-core invertebrate predators like ants. Eisner suggests that the “headstand” routine may serve as a warning to would-be attackers to leave Eleodes alone or suffer the irritating consequences. It appears that at least one crafty desert predator, the grasshopper mouse, has devised a way to circumvent the beetle’s defense. Upon encountering its prey, the grasshopper mouse flips the beetle around and jams the beetle’s rear end into the soil. With the beetle’s chemical defenses shooting harmlessly into the dirt, the grasshopper mouse consumes the beetle starting with the head. When it comes to dining on Eleodesbeetles, the grasshopper mouse has learned that one bad turn deserves another.
We thank Mike and Brian for the inspiration for this Bug of the Week. The wonderful book “For Love of Insects” by Thomas Eisner was used as a reference for this episode.