Cyrnellus fraternus

Larvae are distinguished by their exclusive association with submerged wood (snags) and absence from nearby sand and mud habitats. Within Polycentropodidae, identification to species requires examination of larval morphology or adult genitalia; the retreat-building behavior on stable woody substrata in flowing water contexts is consistent with this species.

Submerged wood (snags) in rivers. Larvae require stable substrata for retreat construction and resistance to periodic high flows. Highest abundances occur on snags with dense deposits of silt and sand. Larvae are absent from soft sand and mud benthic habitats adjacent to submerged wood. More abundant in river reaches with reduced flow than in high-velocity sections.

North America (Nearctic region). Documented from the Elm Fork of the Trinity River, Texas. GBIF records indicate presence in Brazil (multiple states) though these may represent misidentifications or require verification.

Adults emerge May through October. Pupae present July through September. Larvae overwinter. Standing stock biomass significantly higher in autumn and summer than in winter.

Multivoltine with minimum of three generations per year. Overwinters as larvae. Pupation occurs July through September. Adult emergence spans May through October.

Larvae build retreats on stable woody substrata. Distribution is restricted to snags; no occupancy of nearby soft sediments. Larvae are more abundant in lower river reaches with reduced flow than in upper reaches with higher current velocities.

Contributes to secondary production in riverine submerged wood assemblages. Estimated annual production of 1,015.4 mg/m²/yr with mean standing stock biomass of 61.24 mg/m². Cohort production/biomass ratio of 4.59 and annual production/biomass rate of 16.58/yr documented for one population.

• Other PolycentropodidaeLarvae of related species may also inhabit snags; C. fraternus distinguished by specific microhabitat preference for snags with dense silt and sand deposits and documented multivoltine phenology in temperate systems.
• Chironomidae (Diptera)Often co-occur in snag assemblages and show similar seasonal abundance patterns; distinguished by Diptera versus Trichoptera larval morphology and different retreat-building behaviors.

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Submerged wood inhabiting macoinvertebrates of the Elm Fork of the Trinity River, Texas: Assemblage analyses, comparisons to the benthic fauna, and a study of Cyrnellus fraternus (Trichoptera: Polycentropodidae)