ABSTRACT. – In the present article, we show the results of a study carried out in a seasonal stream where several taxa of Plecoptera and Odonata coexist. We analyzed the diet of selected top predators within these macroinvertebrate groups during a whole hydrological year and we studied the possible variations of diet with size. Moreover, we quantified their niche breadth and diet overlap. The results show that only in two taxa, one stonefly and one dragonfly, ontogenetic shifts in diet occur. The stonefly (Isoperla morenica) reduces its intake of animal matter with size and the dragonfly (Onychogomphus forcipatus) increases it. From a trophic niche point of view, all the studied taxa show a relatively narrow niche considering only prey (discarding non-animal resources), and a high niche overlap. This could lead to competition among them, but the fact that they are coexisting in this relatively adverse environment suggests that this is not the case and that prey are not limiting.