This week I had an interesting encounter with a gaggle of magnificent beetles commonly called theAmerican Rhinoceros beetle, Xyloryctes jamaicensis. These giants of the beetle world belong to a large clan known as scarabs that include other featured guests of Bug of the Week such as Japanese beetles and Hercules beetles. While excavating plants near Heatherwick, Maryland, we discovered dozens of large rhinoceros beetles churning the soil beneath trees.
Finding one or two of these beauties on the forest floor is not unusual, but to see so many in one place made ardent bug geeks pause and take notice. The American Rhinoceros beetle is distributed in the United States from New England to Arizona, but in many locations it is considered rare. Adults are reported to eat the leaves of deciduous trees. The larvae are called grubs and they live in leaf litter and soil where they eat decaying organic matter. One study found decaying wood to be a critical component of their diet and suggested that the grubs play an important role in recycling fallen trees. Others have reported grubs eating the roots of woody plants as well. Although we did not witness the remarkable remains of meals left behind by larvae of the rhinoceros beetles, one scientist found that large larvae deposited pellets almost one quarter inch in length after their meals. Unlike deposits left behind by furry creatures such as dogs and cats, pellets of the rhinoceros beetle may take more than seven years to disintegrate on the forest floor. It’s a wonder that some forests are not entirely covered by pellets of these creatures. Like their cousins the Hercules beetle, male Xyloryctes have a magnificent long horn on the front of their head from whence they get their name. Demure females lack this remarkable feature. I wonder if males use this horn to grapple with each other as they battle for resources and mates or if the horn is merely a way to impress the ladies. Whatever its function, it is an impressive appendage indeed.
We thank Dick Bean and our friends at the Maryland Department of Agriculture for providing the inspiration for this episode. The interesting article “The Rhinoceros Beetle, Xyloryctes jamaicensis Drury (Coleoptera, Scarabaeidae): A Locally Abundant Detritivore of a Kansas Riparian Forest” by T. R. Seastedt was used in preparing this story.