Cremastocheilus planatus

Distinguished from other Cremastocheilus by flattened, angular body with dense, pitted exoskeleton. The combination of reduced mandibles, enlarged shield-like mentum, and modified piercing maxillae is diagnostic for the genus. Specific identification of C. planatus requires examination of subtle morphological differences in body proportions and surface sculpturing; the species is being revised taxonomically. Separated from other myrmecophilous beetles by scarab-like antennae with lamellate club and overall scarabaeid body plan.

Associated with ant colonies, particularly mound-building species. Found within nest structures and surrounding soil. Host nests provide protected environment with stable microclimate and food resources.

Nearctic region: recorded from Arizona, California, New Mexico, and Texas. Neotropical region: recorded from Sonora, Mexico. Distribution follows that of host ant species, particularly Formica mound-builders.

Adults disperse to find new host colonies during spring. New adults emerge from pupal cells in late summer or early fall, then slowly move to nest centers to overwinter. Active feeding on ant brood resumes in spring.

Adults are obligate predators of ant larvae and pupae. Larvae feed on decaying vegetation composted by host ants within nest mounds.

• Formica - hostprimary host genus; mound-building species
• 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

Female lays eggs singly in soil around periphery of ant nest mound. Larva passes through three instars, feeding on decaying vegetation composted by ants. Larvae defend against ant attacks by striking with 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 migrate to nest center, acquiring colony scent during transit. Adults overwinter in host nests, becoming active predators in spring.

Adults employ death-feigning (thanatosis) to gain entry to ant colonies: remain motionless with legs outstretched in areas trafficked by worker ants, eliciting retrieval behavior. Once inside, adults move slowly to nest center, accumulating colony odor to avoid detection. Adults are fast, capable fliers but crash-land in areas frequented by scouting ants. Larvae actively defend against ant aggression using mandibles and chemical secretions.

Predator within ant colonies, exerting top-down pressure on host brood populations. May regulate host colony growth or serve as selective pressure on host ant behavior and nest defense. As larvae, contributes to decomposition of organic matter within nest ecosystems.

Occasionally encountered by entomologists and naturalists excavating ant colonies. Subject of scientific interest due to specialized myrmecophilous adaptations. No known economic importance.

• Other Cremastocheilus speciesSimilar myrmecophilous lifestyle, body form, and adaptations; distinguished by subtle differences in body proportions, surface sculpturing, and geographic distribution. The genus is undergoing taxonomic revision.
• Other myrmecophilous StaphylinidaeAlso inhabit ant colonies as social parasites, but differ in body plan (elongate, flexible), antennae form (filiform, not lamellate), and feeding mechanisms (primarily elicit regurgitation rather than predation on brood).

• myrmecophily
• myrmecophagous
• predator
• scarab
• Formicidae
• thanatosis
• social parasite

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• Bug Eric: Anteater Scarab Beetles
• Ants invade Beetles in the Bush! | Beetles In The Bush
• Bichos Argentinos #10 – Friday Formicine | Beetles In The Bush