Cremastocheilus depressus

Distinguished from other Cremastocheilus species by its flattened, angular body form and heavily sculptured exoskeleton with pits and wrinkles. The combination of small size (~10 mm), dull black coloration, and presence of pronotal trichomes helps separate it from similar myrmecophilous beetles. Species-level identification within Cremastocheilus requires examination of detailed morphological characters; the genus is currently undergoing taxonomic revision.

Small, flattened beetle approximately 10 mm in length with a dull black, heavily armored exoskeleton. Body is angular and depressed in profile. Exoskeleton surface is exceedingly dense, often with pits or wrinkles, or both. Antennae normally protected in grooves under the head. Hind angle of pronotum bears special brush-like hairs (trichomes) attached to glands of unknown function. Mentum enlarged and shield-like, covering other mouthparts from below. Maxillae modified into sharp appendages for piercing soft cuticle of ant larvae and pupae. Mandibles reduced, functioning only to help transport liquid food.

Associated with ant nest mounds, particularly those of mound-building Formica species (thatching ants) in prairie and open woodland habitats. Found in "goat prairie" remnants in Wisconsin. Beetles occur within the nest structure itself, from periphery where eggs are laid to central chambers where adults feed.

North America. Documented from Wisconsin in "goat prairie" remnants. The genus Cremastocheilus reaches greatest diversity in the desert southwest, but species occur across much of North America north of Mexico.

Adults disperse to find new hosts during spring, with peak activity when scouting ants are active. New adults emerge from pupal cells in late summer or early fall. Winter is spent within ant nests in a dormant state alongside the host ant colony.

Adults are specialized predators of ant larvae and pupae. Larvae feed on decaying vegetation that ants have composted within the nest mound.

• Formica - hostPrimary host; mound-building thatching ants
• Myrmecocystus - hostHoneypot ants
• Lasius - hostCornfield ants
• Camponotus - hostCarpenter ants
• Pogonomyrmex - hostHarvester ants; southwestern US
• Veromessor - hostHarvester ants; southwestern US
• Aphaenogaster - hostSpine-waisted ants; southwestern US

Females lay eggs singly in soil around the periphery of the ant nest mound. Larvae progress through three instars, feeding on composted vegetation within the nest. Larvae can defend themselves by striking attacking ants with their jaws and secreting repulsive liquids from mandibular and anal glands. Pupation occurs in oval chambers constructed from soil particles. Complete cycle from egg to adult takes approximately four months. Newly emerged adults move slowly toward the center of the nest, accumulating colony scent along the way.

Adults employ death-feigning (thanatosis) to gain entry to ant nests: they become motionless with legs outstretched in areas trafficked by worker ants, and are carried into the nest as presumed food items. Once inside, adults are largely ignored by host ants. Adults fly well and fast but crash-land in areas frequented by scouting ants during dispersal. Adults and larvae are capable of fighting back when attacked. Newly emerged adults acquire colony odor by slow movement through nest passages, rendering themselves chemically incognito to host ants.

Predator within ant colonies, feeding on ant brood. Functions as a social parasite that exploits the resource acquisition and sharing abilities of ant colonies. Larval feeding on composted nest vegetation contributes to nutrient cycling within the nest ecosystem.

Of interest to entomologists studying myrmecophily and social parasitism. Rarely encountered by the general public due to concealed lifestyle within ant nests. Not considered economically significant.

• Other Cremastocheilus speciesShare myrmecophilous lifestyle and general body form; species-level identification requires detailed morphological examination as the genus is undergoing revision
• Other myrmecophilous StaphylinidaeAlso live in ant colonies but differ in body shape (more elongate, flexible), and typically elicit regurgitation from workers rather than preying on brood directly

• myrmecophile
• social parasite
• predator
• scarab beetle
• ant nest inhabitant
• thanatosis
• death-feigning

• BugGuide
• iNaturalist taxon
• Bug Eric: Anteater Scarab Beetles
• Ants invade Beetles in the Bush! | Beetles In The Bush
• Insects, DNA, and Pathogen Extracts Available to Borrow From NEON Biorepository