Individual body size can explain a broad array of ecological patterns, including relative abundances, spatial distributions, and diversity of species. Body size underlies the patterning of energy fluxes and responses to perturbations in food webs, and plays a crucial role in individual life histories as it affects many ecological processes including competition, predation, intraguild predation, and cannibalism.This project will be centred on a mutually illuminating use of theory and experiments. Its main objective is to develop and analyze size-structured models of population dynamics and life history evolution of predatory freshwater insects in small fishless water bodies, with emphasis on a strong mechanistic underpinning for all ecological and evolutionary processes accounted for in the models. I will also carry out laboratory experiments and collect data to be able to corectly parameterize the models, and test the applicability of probabilistic reaction norms to measure selected life history traits in predatory freshwater insects.The application of size-structured models and probabilistic reaction norms are novel in the context of freshwater insects, and both methods can improve our understanding of the ecological and evolutionary processes that shape the individual life histories and population dynamics of this important part of freshwater food webs.