Pest profile

Horned Passalus

Odontotaenius disjunctus · Coleoptera: Passalidae[3]

The horned passalus, also called betsy beetle or bessbug, is a large, glossy black beetle that lives in families inside rotting hardwood logs; it is harmless to people and is not a pest of buildings.[1][2]

Glossy black horned passalus beetle with grooved wing covers on a rotting log
Glossy black horned passalus beetle with grooved wing covers on a rotting log. (c) Dominic, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Adults are glossy black, up to 1 1/2 inches long, with deep grooves along the wing covers and a small horn on top of the head that curves forward.[1][2]
  • Antennae are short and comb-like.[2]
  • Grubs are slender and pale with a light brown head, living in tunnels with the adults.[1][2]

Where it lives

Bess beetles live in decaying hardwood logs; NC State and Clemson describe them in North and South Carolina forests and yards.[1][2]

US map: public records from 28 states since 1990 (GBIF).

Biology and life cycle

A male and female pair up in early spring, tunnel into a decaying log and raise their young together; females lay 30 to 70 eggs, and each pair may raise 20 to 35 new beetles.[1][2]

Adults and grubs eat rotting wood and their own feces, which is enriched by microbes; grubs depend on their parents for food and reach adulthood in about three months.[1][2]

New adults stay in the log until the following spring, and adults can live up to a year or more.[1][2]

Adults and grubs communicate with audible squeaks, and adults squeak when picked up.[1][2]

Damage and signs

  • They break down decaying wood and logs only and are not a pest of urban structures.[1][2]

Health risk

None; they are harmless to people.[1]

Control

Prevention

No control is needed; they are beneficial recyclers of dead wood.[1][2]

Common questions

What is the big shiny black beetle in my firewood?
Often a horned passalus (betsy beetle), which lives in decaying hardwood logs.[1][2]
Do betsy beetles damage houses?
No. They only decompose decaying logs and are not a pest of structures.[1]
Why does the beetle squeak?
Adults rub a rough spot on the abdomen against the wing covers; families communicate with these squeaks.[1][2]

Sources

  1. NC State Extension, “Betsy Beetle or Horned Passalus (PDIC Factsheet).” content.ces.ncsu.edu/horned-passalus-or-betsy-beetles (accessed 2026-10-15)
  2. Clemson Cooperative Extension, Home & Garden Information Center, “Bess Beetles (HGIC factsheet).” hgic.clemson.edu/factsheet/bess-beetles/ (accessed 2026-10-15)
  3. iNaturalist, “Odontotaenius disjunctus taxon page (order and family).” www.inaturalist.org/taxa/122214 (accessed 2026-10-06)

Updated 2026-10-15. Built from sourced records. Spot an error? Tell us.