Bess beetles (Family Passalidae) are wood-dwelling, socially active beetles with around 500 species worldwide. They often live in decaying wood in forests. Burrowing through the decaying wood, they form “galleries” (tunnels inside the wood) below the bark. They live in these small spaces eating, mating, and protecting their larvae and pupae.
Identification
Adult bess beetles have shiny, hard exoskeletons and range from dark brown to black in color. Their elytra (the hard outer coverings on the back portion of a beetle’s body that protect the wings) are lined with grooves running parallel with their body. Small, comb-like antennae help them find food and detect different chemical signals. Larvae have a distinct head and six legs. The bodies are translucent, appearing dark near the head and whiteish to tannish in color towards the rear.
Life Cycle
Bess beetles undergo complete metamorphosis, meaning they have egg, larva, pupa, and adult life stages. In a decaying hardwood log in early spring, an adult male and female will form a pair, create tunnels (by chewing and digging), and mate. Females will lay between 30 and 70 eggs, hatching into larvae within a few weeks. By early fall, the larvae are ready to become pupae. The adults help them by covering them with wood shavings, forming a pupal chamber. After around 2 to 4 weeks, they emerge as adults, though their exoskeletons are not fully hardened yet, so they continue to live protected inside the log. In spring, after their exoskeleton has fully hardened, they emerge from the log to find a mate and the process begins again.
Ecology and Habitat
Bess beetles live in decaying hardwood logs. They construct tunnels in these logs in which they can live for several years, having little to no reason to leave. They feed on the rotting wood and also their own frass (poop)! They do this to keep certain microbes inside their digestive tract, which helps them digest the rotting wood. They are unique in that both adults and larvae live together as families inside the log until the larvae become adults and leave in the spring to find new logs to start their own families. They even communicate audibly (using little squeaks), and even humans can hear them.
Nature’s Recyclers
Bess beetles are beneficial to forest ecosystems because they recycle dead wood, returning nutrients back into the soil. These nutrients can then be used by other plants and other insects. Bess beetles and other recycling insects are critical components of natural ecosystems.
Originally published 10/24