In Cartier Creek, a small stream in southeastern Ontario, larvae of the chironomid Nanocladius branchicolus Saether were found associated symphoretically with nymphs of the damselfly Argia moesta (Hagen). This is the first report of a symphoretic association involving A. moesta; however, N. branchicolus was previously found associated symphoretically with nymphs of stoneflies in the families Perlidae and Pteronarcyidae. The attachment site of the chironomid was most frequently along the abdomen and metathorax of the host, although occasionally they were attached to the prothorax or gill lamellae. Approximately 22% of the population of A. moesta harboured symphoretic chironomids. Lake-outflow streams provide important habitat requirements of N. branchicolus. The benefits to N. branchicolus of a symphoretic habit may include increased stability in fast currents, reduced energy expenditure for relocation, reduced interspecific competition for food and a superior pupation site.