Abstract
In this study, the distribution and occurrence of backswimmers in 21 fishless ponds was analysed in the Nahuel Huapi National Park (Patagonia, Argentina). We performed laboratory experiments to study the impact of different developmental stages of the endemic backswimmer Notonecta vereertbruggheni on typical co‐occurring prey. We recorded three species of backswimmers N . vereertbruggheni , Notonecta virescens and Notonecta fazi . A seasonal study in Fantasma pond showed that adults of N . vereertbruggheni colonise and reproduce in the pond in spring and summer, co‐occurring with other macroinvertebrates and endemic tadpoles. Predation experiments explored the impact of N . vereertbruggheni on two large co‐occurring prey, the calanoid copepod Parabroteas sarsi and the tadpoles of Pleurodema thaul . The backswimmer consumed more copepods than tadpoles when prey was offered separately. Selectivity experiments demonstrated that the copepods were preferred over the tadpoles. Backswimmers may impact the typical assemblages of organisms found in fishless ponds of Patagonia during spring and summer.