Even bacteria have enemies – in water, for example, single-celled ciliates preferably feed on microbes. The microbes protect themselves against predators by employing a variety of tricks, which the ciliates, in turn, attempt to overcome. There ensues an evolutionary competition for the best attack and defence mechanisms. According to scientists from the Max Planck Institute for Evolutionary Biology in Plön, prey such as bacteria have, in the long run, no choice but to maintain protection mechanisms, even if the effort involved is so high that they can barely produce offspring.