Three populations of Glossosoma nigrior Banks (Trichoptera: Glossosomatidae) were compared to determine how differences in thermal regime might affect their life history as well as the growth of individuals within each population. Two populations were located in Big Stony Creek (Stations 1 and 2) while the third was located in Sinking Creek (Station 3). The thermal regimes at each station differed in their seasonal patterns of temperature change and the amount of heat accumulated annually. Aside from a brief period during the spring, Station 1 was the coolest, Station 2 was intermediate, and Station 3 (Sinking Creek) was the warmest of the three sites. Populations of G. nigrior at Stations 2 and 3 ex- hibited typical bivoltine life histories. However, the population at Station 1 was univoltine with larvae present only during the summer. Comparisons among the three summer cohorts present at each station indicated that individuals growing under cooler thermal regimes were larger and grew more rapidly than did individuals exposed to warmer temperatures. A similar pattern was observed between the winter and summer cohorts located at Stations 2 and 3; members of the winter cohort at each station attained higher final dry weights and entered the prepupal stage more rapidly than did their summer cohort counterparts. The larger body size attained by G. nigrior living under cooler thermal regimes suggests that this trichopteran is metabolically more efficient at cooler temperatures. With less of its metabolized energy being allocated for maintenance costs, a large individual may channel more energy towards reproductive efforts. The flexibility in voltinism and differing body size (and thus reproductive capacity)of each cohort are advantageous life history features that have allowed G. nigrior to inhabit areas that may be only thermally suitable for this species during certain periods of the year. This ability to adjust its life history strategy to thermal conditions of a given habitat has allowed G. nigrior to expand its geographic distribution from cool mountain streams to warm water lotic habitats. / Ph. D.