Cremastocheilus armatus

Distinguished from other Cremastocheilus by specific pronotal armature in males. Differs from non-myrmecophilous scarabs by combination of reduced eyes, shortened elytra exposing abdomen, and dense abdominal trichomes. Most reliably identified by collection from ant nests. Separation from other Cremastocheilus species requires examination of male pronotal horn morphology and geographic distribution.

Small, dull black beetle approximately 10 mm in length. Body strongly flattened and angular with exceedingly dense exoskeleton often bearing pits or wrinkles. Elytra shortened, exposing most of the abdomen. Abdomen with dense trichomes (setae) on tergites. Eyes reduced. Males possess prominent horns on pronotum; females lack these horns. Antennae normally protected in grooves under head.

Strictly myrmecophilous; found exclusively within nests of host ants. Associated with mound-building Formica species and other ant genera in western North America. Occurs in ant nest interiors and immediate periphery where eggs are laid.

Western North America: recorded from California, Idaho, Montana, Nevada, Oregon, and British Columbia. Distribution corresponds to range of host ant species in this region.

Adults present in ant colonies year-round. Dispersal flights to locate new host colonies occur in spring. New adults emerge from pupal cells in late summer or early fall.

Feeds on liquid food obtained from host ants through trophallaxis or by soliciting regurgitation from workers. Adults do not consume solid food; mandibles reduced and function only to transport liquid to mouth.

• Formica species - hostmound-building species, primary hosts
• Myrmecocystus - hosthoneypot ants
• Lasius - hostcornfield ants
• Camponotus - hostcarpenter ants

Complete metamorphosis. Females lay eggs singly in soil around nest periphery. Larvae feed on decaying vegetation composted by ants, progressing through three instars over approximately four months. Larvae defend against ant attacks with striking mandibles and repulsive secretions from mandibular and anal glands. Pupation occurs in oval chambers constructed from soil particles. Adults emerge in late summer or fall, move to nest center to acquire colony scent, and remain dormant through winter. Spring activation triggers feeding on ant larvae and pupae using modified maxillae to pierce soft cuticle.

Employs death-feigning (thanatosis) to gain entry to ant nests: remains motionless with legs outstretched in areas trafficked by scouting workers, enabling discovery and transport into nest by ants as presumed food items. Adults move freely within colonies without eliciting aggression, presumably through chemical integration. Acquire colony scent by slow movement to nest center after emergence. Feeds on ant brood using specialized piercing-sucking mouthpart modifications.

Myrmecophilous inquiline occupying intermediate position between commensalism and parasitism. Integrates into ant colony food web as recipient of liquid resources and predator of ant brood. Population densities vary: typically 20-30 individuals per excavated nest, occasionally up to 200.

No direct economic or medical significance. Of scientific interest as example of extreme myrmecophilous specialization and convergent evolution with other ant-associated beetles.

• Other Cremastocheilus speciesShare myrmecophilous lifestyle and general body plan; distinguished by male pronotal horn morphology and geographic range
• Non-myrmecophilous CetoniinaeDiffer in complete elytra covering abdomen, well-developed eyes, lack of abdominal trichomes, and free-living habit

• myrmecophile
• inquiline
• scarab beetle
• ant associate
• sexual dimorphism
• thanatosis

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• Bug Eric: Anteater Scarab Beetles
• Europe’s most complete stegosaurian skull unearthed in Spain
• Ants invade Beetles in the Bush! | Beetles In The Bush
• Notes on the Life Cycle and Myrmecophilous Adaptations of Cremastocheilus Armatus(Coleoptera: Scarabaeidae)