Insects living in freshwaters possess a suite of adaptations in the aquatic larval and terrestrial adult phase. In this review, we suggest that there are three key aspects of the freshwater habitat templet that forge different sets of ecological traits in adults, (i) For most aquatic insects, the evolutionary stability of freshwaters reduces the need for adult dispersal and its associated morphological and physiological adaptations. For herbivorous species, the paucity of freshwater angiosperms favours dietary generalists, further mitigating against the evolution of highly developed dispersal adaptations to locate larval food plants, (ii) For species with obligate predatory juveniles, principally the Odonata and the larger predatory Coleoptera and Hemiptera, the discrete nature of freshwater habitats may generate intraspecific competition for prey resources, leading to density-dependent mortality. This may drive the evolution of advanced adult feeding, dispersal and oviposition strategies to maximize survival and growth of aquatic nymphs, (iii) Discrete water bodies attract a spatially predictable supply of terrestrial animals to drink, favouring the evolution of blood-feeding behaviour in adults of the aquatic Diptera. The high-quality adult dietmay allow these dipterans to colonize small, ephemeral habitats and habitats with poor larval resources.
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