Alone on a swampy trail, I noticed a half-inch beetle feeding on a mushroom. It was gray and bumpy, resembling tree bark.
I was lucky to sight the Horned Fungus Beetle (Bolitotherus cornutus), since it’s active at night. This particular morning was overcast and the lighting was dim, which led this individual to indulge in an extended meal.
The insect pictured is a male, since only males have horns protruding from the thorax. These are used to wrestle other males from females during courtship. They’re also used to defend territories. The Horned Fungus Beetle may live on the same decaying tree, among brackets of shelf-mushrooms, for nearly a decade, matching the beetle’s lifespan.
During the summer, females lay less than a dozen eggs, one at a time. Each egg is deposited on a mushroom and covered with a dark secretion. When the egg hatches 16 days later, the larva stays inside the egg for several days more. It then feeds by tunneling into and through the fungus. Young overwinter within the fungus and emerge the following year.
Usually larvae avoid one another. However, if a larger youngster encounters a smaller one, the weaker animal may be devoured. Should a larva die within the mushroom, the fungus grows around and into the deceased’s body.
When disturbed, an adult Horned Fungus Beetle folds its legs and plays dead. However, if a mammal breathes on it, it secretes droplets of irritating chemicals that smell bad and burn the mouth.
The Horned Fungus Beetle is beneficial to several species of mites. Most of these mites eat fungal spores, but hitchhike a ride (or catch a flight) to get around.