Current Issue

Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Recyclers in the circle of life - Bess beetles, Odontotaenius disjunctus


Powerful jaws and a magnificent horn are standard equipment for a bess beetle. 


During the past week or two while wandering some wooded trails, I have enjoyed several encounters with magnificent bess beetles as they scurried about the forest floor. Bess beetles are also known as patent leather beetles and the horned Passalus by virtue of their shiny deep brown color and notable horns. These powerful beetles are important participants in the great circle of life. No, they do not occupy an exalted place at the top of the food chain like Mufasa, the Lion King. They sit near the bottom of the heap along with fungi and bacteria where they help decompose fibrous wood.

Adult bess beetles use strong jaws to gnaw and ingest wood. After being processed in the beetle’s digestive system and deposited back in the wood, the microbe-packed droppings are consumed by bess beetle larvae. The microbes contained in the leavings of the adult beetles are particularly important for young larvae that require the microorganisms to help them digest wood and obtain nutrients from tough plant tissues such as lignin and cellulose.

Upon plucking one of the beetles from the forest trail, I was intrigued to hear it squeak. Bess beetles are able to produce sound by rubbing their wings across a rasp-like structure on the upper surface of their back just beneath the hard wing covers. This form of sound production is called stridulation. Many beetles, such as the milkweed longhorned beetle we met on July 3, 2006 in “Hooray for the red, white, and blue!”, stridulate. The larvae of bess beetles are somewhat unique in that they also stridulate by rubbing together two sections of their legs. Several authors suggest squeaking sounds enable both larvae and adults to communicate with others in the decomposing wood. One account indicates that larvae follow the calls of adults in the colony. Perhaps this is a way for parents to assist their babies in discovering food or maybe it conveys a message akin to “eat your vegetables.” Other scientists believe the calls may frighten would-be predators. To learn the true nature of the call of the bess beetle, I made a recording of the sound. By playing the sound backward at very slow speed, the beetles could clearly be heard singing the Gershwin classic “summer time and the livin’ is easy.” In this year of exceptionally warm weather, I took this as a sure sign that summer is not far off. 

Decomposing wood is the realm of the bess beetle.



Information for this Bug of the Week came from a paper written by L.E. Gray in 1946 entitled “Observations on the life history of the horned Passalus”.

For more information on bess beetles, please visit the following web site: