Cremastocheilus constricticollis

Distinguished from other Cremastocheilus species by the constricted base of the pronotum, the feature referenced in its specific epithet. The combination of small size (approximately 10 mm), dull black coloration, flattened angular body, and heavily sculptured exoskeleton separates it from most other scarab beetles. Within its genus, precise identification requires examination of pronotal shape and degree of constriction. The presence of trichomes on the pronotal hind angles is shared with congeners and does not alone distinguish species. Geographic occurrence in Arizona and New Mexico helps narrow identification possibilities, as Cremastocheilus species show regional differentiation.

Associated with ant nest mounds, particularly those of mound-building ant species. In the southwestern United States, has been documented with harvester ants (Pogonomyrmex, Veromessor) and spine-waisted ants (Aphaenogaster). The beetles occur in the periphery and interior of ant nests, with larvae developing in soil around nest mounds and feeding on decaying vegetation that ants have accumulated. Adults are found within ant colonies during winter dormancy and become active in spring.

Known from Arizona and New Mexico in the southwestern United States. GBIF records indicate occurrence in these two states within the Nearctic region. The species is part of a genus that reaches greatest diversity in the desert southwest, though individual species ranges are often restricted.

Adults emerge from pupal cells in late summer or fall, then disperse to locate new host ant colonies. This dispersal period represents the primary time when adults may be encountered outside ant nests. Adults overwinter within ant nests in a dormant state. Spring marks the resumption of feeding activity on ant larvae. The complete cycle from egg to adult takes approximately four months.

Adults are specialist predators of ant larvae and sometimes pupae, piercing the soft cuticle with modified maxillae and consuming internal fluids. Larvae feed on decaying vegetation that ants have accumulated and partially composted within their nest mounds.

• Pogonomyrmex - host antharvester ants, frequent host in southwestern U.S.
• Veromessor - host antharvester ants, frequent host in southwestern U.S.
• Aphaenogaster - host antspine-waisted ants, frequent host in southwestern U.S.

Females lay eggs singly in soil around the periphery of ant nest mounds. Larvae progress through three instars, feeding on decaying vegetation within the ant mound and capable of defending themselves against attacking ants by striking with their jaws and secreting repulsive liquids from mandibular and anal glands. Larvae pupate in oval chambers constructed from soil particles. Adults emerge in late summer or fall, accumulate colony scent while moving slowly to the nest center, and remain dormant through winter. The generation time from egg to adult is approximately four months.

Adults employ death-feigning (thanatosis) to gain entry to ant nests: they become motionless with legs outstretched in areas trafficked by scouting worker ants, which carry the apparent carcass into the nest. Newly emerged adults move slowly to the nest center to acquire colony-specific chemical cues, rendering them chemically inconspicuous to host ants. Adults are capable of strong, fast flight during the dispersal period but crash-land in locations frequented by scouting ants.

Acts as a specialized predator within ant colonies, consuming ant brood. Larvae contribute to decomposition of organic matter accumulated by ants. The relationship is parasitic rather than mutualistic, with beetles exploiting the resource concentration and protective structure provided by ant colonies.

No direct economic importance. Of interest to entomologists studying myrmecophily and the evolution of specialized host-parasite relationships. Rarely encountered by the general public due to cryptic lifestyle within ant nests. May be found when excavating ant colonies under stones or boards.

• other Cremastocheilus speciesshare myrmecophilous lifestyle, death-feigning behavior, and morphological specializations; distinguished by pronotal shape, geographic range, and host associations
• other Cetoniinae scarabsmost lack the flattened angular body form, dense sculptured exoskeleton, and myrmecophilous adaptations; do not occur within ant nests

• myrmecophile
• parasite
• predator
• death-feigning
• thanatosis
• scarab beetle
• ant nest
• southwestern United States

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• Bug Eric: Anteater Scarab Beetles
• Ants invade Beetles in the Bush! | Beetles In The Bush