Bolitotherus cornutus

Excerpt from the book Stalking the Vesper Bluets

by Stephen Cresswell


Forked Fungus Beetles live in and on a shelf fungus called Artist's Conk (artists sometimes gather the fungus and etch designs on its white undersurface). While the beetles may occasionally walk onto the log on which the fungus is growing, most of their growing and eating and mating and egg-laying happen on the upper or lower surface of the shelf fungus, or inside the fungus.

These beetles measure about 10 mm long, less than half an inch. The males have a large pair of bristly horns, while the females have a low pair of tubercules. They are found all over the eastern United States and across the border into Canada.

Female entomologists were among the first to study the Forked Fungus Beetle in the field. One path-breaking study was published in 1956, as Magdalene Pferrer Liles compared the life history of populations in Ohio and in Michigan. Her study was followed up by Ann Pace of the University of Michigan, who did a more exhaustive field study published nine years later.

For her study, Pace lived among the Forked Fungus Beetles along Michigan's Huron River in 1965 and 1966. She was the Dian Fossey of the beetle world. Her dedication to her subjects is especially remarkable when we acknowledge that Forked Fungus Beetles are nocturnal: Pace made most of her observations between 9 p.m. and 3 a.m.

By marking individuals with paint, Pace was able to prove that this species of beetle often lives more than one year, and that in fact females sometimes lay eggs in two consecutive spring seasons. At the time only a couple of other beetle species were known to live more than a year as adults.

As Pace watched in the middle of the night, she would see pairs of copulating beetles. Then, six times, she saw a lone male beetle approach the happy couple and use his horns to try to push the other male off the female, off the fungus, and off the log. Two of six times the interloper succeeded, but in the other four cases the attacked male hung on and refused to be dislodged.

On several other occasions Pace watched territorial males use their horns to dump other males, even when no female was nearby. Pace kept a special eye on one such territorial male on Fungus Number 5. She found that over a two month period he never moved more than eight inches from his favorite spot, "except for a one hour period on 30 July" when he apparently ran a quick errand.

Bolitotherus cornutus, preliminary to mating

During courtship preliminary to mating, Pace watched as the male Forked Fungus Beetle climbed on top of the female, in a reversed position (the male's head above the female's abdomen)—the same position seen in the photo at left. The male rubbed his underside against the two small tubercules behind the female's head. The result was a rasping sound that the beetles apparently found to be a turn-on.

I picture Ann Pace, hearing this music at 2 a.m., and carefully standing various distances away, so she could verify Lile's statement that the rasping was "audible at a distance of six to eight feet from the fungus."

Since so few people are standing within six to eight feet of a shelf fungus in the forest at 2 a.m., Liles and Pace are surely among the very few people who have ever heard the cry of the Forked Fungus Beetle. I sometimes consider taking a sleeping bag into the woods and passing the night near a shelf fungus so that I, too, might enter this select fraternity. My curiosity has been piqued. I'd like to know what this mating call sounds like.

With my luck I would sleep through it, dreaming perhaps of using a rasp in eighth grade shop class.