Coelocnemis rugulosa

Distinguished from Eleodes by the presence of two parallel lines of yellow pubescence on the inner surface of the tibiae (Eleodes lacks this feature). The pronotum is typically broader and more angular than in Eleodes. From other Coelocnemis species, identification requires examination of more subtle characters; C. rugulosa specifically is characterized by its sculptured (rugose) elytra, as suggested by the species epithet. Found in pine forest and oak-conifer woodland habitats rather than barren desert ecosystems.

Large, robust black beetle with fused elytra and no flight wings. Pronotum broader and more angular than in Eleodes. Hind tibiae bear distinct parallel lines of yellow pubescence on their inner surfaces, with a groove between them (the "hollow shin" characteristic that gives the genus its name). Body form typical of darkling beetles: elongate, somewhat cylindrical, with elytra completely covering the abdomen.

Pine forest habitats and oak-conifer woodlands. Typically found in or under rotten logs. Occupies mesic to xeric forest environments in mountainous regions of western North America.

Western United States and adjacent southern Canada. Specific records include southwestern U.S. including Utah, Arizona, and Nevada. The genus Coelocnemis as a whole ranges across western North America; C. rugulosa has been documented from at least Utah based on collection records.

Adults active during warmer months. Nocturnal activity peaks during summer. One observation from September in southwestern Utah suggests late-season activity. Hibernates in small groups in dry, protected niches during winter.

Adults feed on plant detritus, lichens, fungi, seeds, and related organic matter.

Larvae resemble large mealworms, armed at the rear with a pair of hook-like prongs and smaller teeth behind them. Larval development occurs in decaying wood and organic matter. Adults are long-lived, surviving at least three years.

Nocturnally active, wandering at night to avoid desiccation and overheating. Performs defensive "headstand" behavior when threatened, raising the abdomen and secreting defensive chemicals from glands at the tip. Defensive secretions are smelly and effectively repel most vertebrate predators. Hibernates in small groups in dry, protected locations.

Contributes to decomposition of plant detritus and nutrient cycling in forest ecosystems. Serves as prey for specialized predators such as grasshopper mice, which have evolved techniques to disarm the beetles by jamming the abdomen into the ground before consuming the head and thorax.

No significant direct human relevance. Not a pest species. May be encountered by entomologists and naturalists in western North American forests.

• EleodesSuperficially similar large black darkling beetles, but Eleodes lacks the parallel lines of yellow pubescence on the inner tibial surface and typically has a narrower, less angular pronotum. Eleodes is more characteristic of barren desert ecosystems rather than pine-oak woodlands.
• Coelocnemis sulcataCongeneric species with similar habitat preferences (pine forest habitats, found on trunks of Pinus ponderosa), distinguished by elytral sculpture and other subtle morphological differences.
• ZopherusAnother large black beetle found on pine trunks at night in similar habitats, but belongs to family Zopheridae (ironclad beetles) and has different body form and defensive strategies.

Commonly mistaken for Eleodes by casual observers due to similar large black appearance and defensive headstand behavior. The genus name Coelocnemis is often misspelled or confused with Coelocnemus (an error seen even in some field notes).

• darkling beetle
• Tenebrionidae
• western North America
• pine forest
• nocturnal
• flightless
• defensive headstand

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• Bug Eric: Big Black Beetles: Coelocnemis
• Uncategorized | Blog - Part 52
• Oecanthidae | Beetles In The Bush