Also known as: Patent Leather Beetle, Bess Bug, Betsy Beetle
Scientific name: Odontotaenius disjunctus (Illiger)
Feeding on rotting hardwoods like elm and oak, these beetles live and breed in the tunnels they create in rotting logs. If a log remains undisturbed, it could become home to more than one generation of Horned Passalus Beetles. Both parents, other adults and even older siblings help take care of new egg clutches.
Horned Passalus Beetles have wings under their shell, which they use to "stridulate" (make shrill sounds by rubbing together). They produce 17 distinct sounds to communicate danger, group messages, and direction for immature beetles within their complex social structure.
Beneficial?
As beneficial decomposers of wood, they feed in two stages - first they chew rotting wood up into "frass" which is easier for bacteria and fungi to decompose - then the beetles eat the frass and the bacteria help the beetle digest it.
The horned passalus only decomposes decaying wood or logs, and it is not a pest of urban structures.
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So are Horned Passalus Beetles ok to leave in the garden?
We're choosing to keep them! We have several logs in the community garden that we use for sitting and setting tools on. These beetles will help them break down into great nutrients for the soil and invite more microflora (naturally occurring fungi and bacteria) into our garden ecosystem!
More info and photos:
https://entnemdept.ufl.edu/creatures/misc/beetles/horned_passalus.htm