Small-scale habitat relationships of Corydalus cornutus hellgrammites in central Ohio riffles

Authors: BOSSLEY, JON - Mount Vernon Nazarene University; Smiley, Peter; HUMPHREY, HANNA - Mount Vernon Nazarene University

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2026
Publication Date: 4/10/2026
Citation: Bossley, J., Smiley, P.C., Humphrey, H. 2026. Small-scale habitat relationships of Corydalus cornutus hellgrammites in central Ohio riffles. Insects. 17. Article 410. https://doi.org/10.3390/insects17040410.
DOI: https://doi.org/10.3390/insects17040410

Interpretive Summary: Larval eastern dobsonflies are large aquatic invertebrates that are an important food source for popular sport fishes in streams and rivers of the Midwestern United States. Additionally, these invertebrates are used as live bait by recreational anglers. Larval eastern dobsonflies are associated with riffles, which are rare habitats in agricultural streams and rivers in the Midwestern United States. Information is lacking on the environmental variables that influence the occurrence, abundance and size of larval eastern dobsonflies within riffles of agricultural rivers in the Midwestern United States. We conducted a two-year field experiment that documented the habitat-relationships of larval eastern dobsonflies within riffles in agricultural rivers in central Ohio. Larval eastern dobsonfly occurrence and abundance increased with water velocity, substrate size, substrate assortment. Additionally, larval body size increased with increasing distances to the nearest plot containing larval eastern dobsonflies. These results represent the first documentation of larval eastern dobsonfly habitat relationships within riffles in agricultural rivers in the Midwestern United States. These results will be of interest to farmers, Soil and Water Conservation Districts, and NRCS staff working to conserve agricultural streams and rivers in the Midwestern United States. Specifically, our results indicate that conservation practices that increase water velocity and substrate size in riffles of agricultural rivers in the Midwest will increase the abundance of larval eastern dobsonflies. Subsequently, these findings will benefit American farmers, their friends and families, and rural communities by providing information that will improve their recreational fishing opportunities within agricultural streams and rivers via Soil and Water Conservation District and NRCS stream conservation efforts. Our results also suggest that larval dobsonflies will be an effective indicator species that can be used to quantify outcomes and approaches used by the NRCS’s Working Lands for Wildlife Aquatic Species Framework and to support NRCS efforts to develop effective conservation strategies to protect and conserve streams, rivers and aquatic species on private agricultural lands.

Technical Abstract: Corydalis cornutus hellgrammites are known to inhabit riffles, but information is scarce regarding their habitat relationships at the plot scale and in the northern part of their range in the United States. We investigated the relationship of C. cornutus hellgrammite occurrence, density, and body size with environmental variables at the 1 m2 plot scale within central Ohio riffles. We collected hellgrammites and measured hydrological, substrate, large instream wood, and canopy cover variables in nine riffles in 2023 and 10 riffles in 2024. Occurrence and density were best predicted by water velocity and grain size score, while none of the measured variables were a good predictor of head capsule width. Occurrence increased with increasing water velocity, grain size score, and substrate richness. Density increased as water velocity, grain size score, substrate richness, and edge-interior scores increased. Head capsule width increased with increasing distances to the nearest plot with hellgrammites. Our results suggest that C. cornutus hellgrammites can serve as an indicator species because their occurrence and density reflect the water velocity and substrate conditions within riffles in the Midwestern United States.