Telmatogeton torrenticola Terry (Chironomidae: Telmatogetoninae) is a large endemic chironomid (last instar sometimes > 20 mm). Larval populations of T. torrenticola were studied over two summers in order to document the habitat, natural history and bioenergetics in relation to stream hydrology at two temporal scales. Reductions in stream flow, either naturally or anthropogenically induced, have complex effects on the larval populations which depend on the magnitude of stream flow at two temporal scales (i.e. long term discharge over months to short term spates) and microhabitat spatial heterogeneity. Habitats of T. torrenticola are in dynamic equilibrium where abiotic factors are the governing forces of the epilithic successional trajectory which consequently affects microhabitat flow environments important for community resistance to spate events. Spates have a regenerating effect on the torrential benthic community and reductions in long term flow decrease the magnitude and frequency of these habitat “regenerating forces.” Larval populations exist in a state of fluctuating stability, governed and dependent upon the unpredictable stream discharge. Larval sexual dimorphism appears to act in a compensatory way resulting in optimal female fecundity, gamete quality and increased probability of encountering reproductive males upon emergence. Based on a multivoltine, asynchronous life-cycle, with continuous reproduction, T. torrenticola has extremely high annual secondary production (expressed as ash-free dry mass, AFDM) ranging from 106,713 - 201,927 mg AFDM · m-2 · yr-1. Based on annual P/B ratios, production is maintained by high standing stock biomass rather than rapid biomass turnover. When stream flow was reduced by ~ 40%, larval bioenergetics in habitats that appear to be optimal in terms of depth and flow are reduced to the same magnitudes of those found in sub-optimal habitats within a year of higher mean stream flow. Reduced water flow due to natural drought or anthropogenic circumstances can create flow and depth conditions similar to those of lower quality microhabitats, which can severely compromise lotic insect bioenergetics with cascading effects throughout the stream food web and trophic structure. The information gained from this dissertation can be applied towards using the Telmatogeton species as possible bioindicators of stream condition.