Most recently reviewed by: Pat Porter (2018)
Common Name(s): Betsy Beetle, Horned Passalus Beetle
Adult beetles are up to 1-3/8 inches long, shining black with a series of grooves running the length of the wing covers (elytra) and a short horn on the front of the head between the eyes. Immature stages (larvae) are similar to “white grubs” (Coleoptera: Scarabidae). However, larvae only have two pairs of true legs and grow to about 1-½ inches long.
Origin and Distribution
The horned passalus occurs in a wide range from mid-Florida to Massachusetts, Southern Texas to Minnesota and Nebraska (Schuster 1983). More recent sources indicate further expansion from eastern Texas, throughout the eastern United States, and from southern Manitoba through the Canadian deciduous forests, and southern Ontario (Arnett et al. 2002).
Passalid beetles are somewhat social insects, with colonies living in galleries (tunnels) in decaying logs and stumps. Wood infested by these beetles is usually well decomposed and falls apart readily. Adult Passalus beetles are often covered by mites. Adults tend and feed larvae, preparing food with salivary secretions. Food consists of decaying plant matter. When disturbed, adults produce a squeaking sound by rubbing their wings on the abdomen. This is apparently used for communication between members of the colony.
Habitat & Hosts
Horned passalus beetles and larvae occur in decaying logs, often in large numbers; considered beneficial in activities to decompose dead wood; medically harmless.
Eggs: Using its large mandibles, the horned passalus cuts into fallen logs and creates galleries where the eggs are deposited and hatch. The eggs are exceptionally large, measuring at 3.0 by 2.4 mm (approximately 0.1 inch) when first laid and reaching 3.7 by 3.2 mm just before hatching. The size of the eggs makes them easy to manipulate in the large mandibles of the adults. Eggs are typically found in groups surrounded by frass from the adults.
Larvae: The larvae are large, white grubs that have up to three instars. Larvae are found in the same galleries as the adults. To obtain nutrients, the larvae feed on predigested wood from the adults.
Pupae: As pupae begin to form they become pearly white with a rainbow sheen. As the pupae age, they lose their rainbow sheen and can range in color from off white to earth-toned. Pupae that are nearing emergence become translucent. Pupation times vary based on climatic conditions.
Adults aggregate and compete for sections of fallen wood, provided the wood is large enough to support more than the initial inhabitants of the wood.
ManagementIf you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.
Horned passalus occurs in decaying logs, often in large numbers, and is considered beneficial in its activities to decompose dead wood. This insect is medically harmless.
Arnett Jr RH, Thomas MC, Skelley PE, Frank JH. (editors) 2002. American Beetles, Volume II: Polyphaga: Scarabaeoidea through Curculionoidea. pp. 861. CRC Press, Boca Raton, FL.
Horned passalus – Odontotaenius disjunctus (Illiger). [online] Available at: http://entnemdept.ufl.edu/creatures/misc/beetles/horned_passalus.htm [Accessed 24 Oct. 2018].
Wicknick JA, Miskelly SA. 2009. Behavioral interactions between non-cohabitating bess beetles, Odontotaenius disjunctus (Illiger) (Coleoptera: Passalidae). The Coleopterists Bulletin 63: 108-116.