The horned passalus belongs to a family of beetles called Bess beetles or patent leather beetles. It’s the only species in the family that lives in Missouri. Bess beetles are black and shiny (like patent leather), and have one lengthwise groove on the pronotum (shoulderlike area between head and wing covers). There are lengthwise grooves on the wing covers, too. The antennae are not elbowed.
The horned passalus has a forward-pointing horn on its head and lives in colonies, with the larvae, in well-rotted wood. Adults and larvae communicate by rasping noises, made by rubbing parts of their bodies together. They often stridulate (make the rasping sound) when picked up, overturned, or otherwise harassed.
The larvae are whitish grubs that live in rotting wood. The heads are brownish, and it looks like they have two pairs of legs (the hind pair is shorter and used to make raspy sounds). They look a lot like the larvae of other beetles.
Length: about 1¼ to 1½ inches (adults).
Habitat and Conservation
Deciduous forests. These beetles live in colonies in well-rotted hardwood logs, stumps, and other decaying wood. The larvae and adults eat wood. Although there are many ant, bee, and wasp species with social lifestyles, it is unusual among beetles. Adults and larvae create winding tunnels in wood and live together in family groups, the adults (both males and females) feeding and tending the larvae, and all communicating via their scratchy rasping noises.
Adults and larvae eat rotting wood of hardwood logs, and the fungi and juices associated with it. Adults feed the larvae by chewing wood to soften it, then giving it to the larvae.
Horned passalus beetles apparently live for more than a year. Although they can fly, adults don’t do it often, tending to stay in the tunnels and galleries in their colony’s home. When they fly, it may be for dispersal and mating, or because they have been captivated by a light. Mating can also take place in the colony. Eggs hatch into larvae that are fed by adults. They grow, molt, pupate, then emerge as adult beetles.
Although capable of delivering a genuine pinch, the horned passalus cannot harm you.
Old-time Ozarkers believed that the "blood" of this beetle could cure an earache. Their general word for this insect was betsey bug.
In one episode of "The Beverly Hillbillies" TV show, Granny Clampett uses a "weather beetle" named Cecil to predict the weather. Perhaps Cecil was a horned passalus. The creator of that show was Paul Henning, a native Missourian who was exposed to Ozark culture. Interestingly, science has shown that at least some insects alter their behavior in response to changes in barometric pressure.
The common name for the family has an interesting history. The word “Bess” apparently arose as a misinterpretation of the French word for “kiss,” baiser (pronounced something like “bayzay”). This might refer to the squeaky, kissy, rasping sounds these insects make, or it could refer to their ability to pinch. The French word baiser became “Bess,” a common personal name in English, which led to other common names, Betsy beetle or Betsey bug.
The species plays an important role in cycling nutrients in rotting logs back into the soil, enriching the earth and helping to clear the forest of fallen timber.
Many animals, including raccoons and woodpeckers, probe or poke through rotting logs and eat the grubs.
Many other animals, including birds, bats, and skunks, frogs, eat the adults, especially when they leave the safety of the colony’s log.
Mites and other parasites feed on adults and larvae, too.