As hydrologic regimes shift under climate change, ephemeral freshwater ecosystems and their aquatic insect communities face increasing instability. Because aquatic insects are sensitive to environmental conditions and fill diverse ecological roles, they serve as useful bioindicators of ecosystem health. I conducted a mesocosm experiment to test whether taxonomic identity or functional trait composition respond more predictably to drying conditions. Using 24 mesocosms, I manipulated surface area and water permanence to simulate variable hydroperiods and sampled aquatic insects over time. I recorded 6,521 individuals from 24 morphospecies and 19 families, dominated by Odonata, Coleoptera, and Hemiptera. Multivariate analyses revealed contrasting patterns. Redundancy analysis showed hydrologic variables explained moderate variation in both taxonomic (adjusted R² = 0.592) and functional composition (adjusted R² = 0.561). Neither hydrologic treatment, nor the interaction factor had a significant effect on taxonomic and functional composition, yet they both changed over time. Overall, my study demonstrates that taxonomic and trait composition appear to follow successional processes in the assembly of aquatic insect communities. Further, despite the lack of a significant relationship between hydrology and functional composition, trait-based approaches can serve as an additional indicator to taxonomy for how communities work under rapidly changing conditions.