Priacma serrata

Distinguished from other North American Cupedidae by the combination of: lateral (rather than dorsal) antennal insertion; four dorsal head protuberances; and male-specific attraction to chlorine/bleach odor. The lateral antennal insertion separates Priacma from all other cupedid genera, which possess dorsally shifted antennae. Males are readily attracted to bleach-soaked materials, a behavior unique among North American beetles. The larger, rarely collected females may be confused with other cupedids but share the same diagnostic head structures.

Males measure 9.6–12.5 mm in length. The body exhibits the reticulated (net-like) elytral pattern characteristic of Cupedidae. Sexual dimorphism is pronounced: females are much larger than males and seldom collected. The head bears four cone-shaped protuberances on the dorsal surface—a diagnostic autapomorphy of the family Cupedidae. The galea is narrow-stalked with a round, pubescent distal galeomere, an adaptation likely associated with pollen-feeding. The mandible retains a plesiomorphic shape compared to related families. The prementum is plate-like and enlarged, forming a lid that closes the mouth when retracted.

Coniferous forests. Adults are found under loose bark of trees. The association with coniferous forests appears consistent across the known range, though specific tree species preferences are not documented.

Western North America. Documented from British Columbia, Canada (near Lumby) and inferred to occur more broadly in western North American coniferous forests. GBIF records confirm presence in British Columbia.

Adult emergence is highly episodic, with sporadic mass emergence events rather than continuous activity. In British Columbia, males were active from early May to early June, with swarming behavior observed on fair days during this period.

Larval stages unknown. Adult males possess withered, non-functional digestive tracts with empty intestines; dissections confirm the gut is too atrophied to pass food. This suggests adults do not feed, though the larval diet and developmental biology remain undocumented.

Males exhibit gregarious flight behavior and strong attraction to chlorine-based compounds, specifically bleach (sodium hypochlorite/sodium chlorate solutions). In the presence of bleach odor, males swarm and fly actively around treated materials. This behavior occurs on fair days and is sufficiently reliable to serve as a collection method. The neurological or sensory basis for this attraction is unknown. Adult emergence occurs in sporadic, synchronized events rather than continuously.

Subject of scientific interest due to its phylogenetic position as a relict archostematan beetle and unique male behavior. The bleach attraction provides a rare example of a chemically-mediated, species-specific behavioral response that can be exploited for monitoring or collection. No economic or pest significance documented.

• Other Cupedidae (Cupes, Tenomerga, Paracupes, etc.)Share reticulated elytra and general body form, but possess dorsally inserted antennae (vs. lateral in Priacma) and lack the four dorsal head protuberances characteristic of Cupedidae including Priacma.
• OmmatidaeRelated archostematan family with superficially similar appearance, but mandibles have vertically arranged apical teeth (autapomorphy of Ommatidae) versus the plesiomorphic mandible shape of Cupedidae; also lack the distinctive head protuberances and bleach-attraction behavior.

• Cupedidae
• Archostemata
• relict species
• sexual dimorphism
• bleach attraction
• chlorine response
• coniferous forest
• western North America
• non-feeding adult
• episodic emergence
• phylogenetic relict
• X-ray tomography
• head morphology
• gregarious flight

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Bembicid Holdings | Entomology Research Museum
• Grasshopper Collections and Survey
• Meloidae Holdings | Entomology Research Museum
• The Elm Zigzag Sawfly is Cute, It's Spreading Fast, and Now It Wants Your Zelkova Trees
• Back-Seat Driver: The Parasite That Makes Bees Drop Off Its Babies
• Head structures ofPriacma serrataleconte (coleptera, archostemata) inferred from X‐ray tomography
• Observations on the Flight, Wing Movements and Wing Structure of Male Priacma serrata (Lee.) (Coleoptera: Cupedidae)