In the life cycle of Blues of the genus Maculinea, ants play an essential role. The whole life cycle has been carefully studied by the author for the Dusky Large Blue (Maculinea nausithous). Experiments were performed in an artificial ants’ nest so that the behaviour of the caterpillars and the ants could be followed at close range. Caterpillars show a strong preference for small larvae. Using special recording equipment, the author was able to pick up the distinctive vibrations produced by caterpillars, and chrysalides. Breeding Dusky Large Blues in an artificial ants’ nest proved to be successful.