The Hymenoptera are an extensive order of the insects, including more than 250,000 species of wasps, bees, ants, ichneumon flies, gall wasps, horntails, and sawflies. These insects are familiar to some extent to everybody who observes nature, but to the naturalist studying the mode of life and the behaviour of insects they are exceptionally interesting. It is not only the high complexity and specialization that usually mark the behaviour of the Hymenoptera but also the tremendous variety of modes of life and instincts found within this one, clearly demarcated order of insects which merits special attention. It presents the investigator with favourable opportunities for examining the genesis of instinctive phenomena, thereby making them easier for us to understand. This fact, valuable in itself, receives added interest because it is extremely important for the understanding of the general course of the evolutionary development of the instincts of the Hymenoptera — its direction, its more important milestones, and even the actual way in which some instincts are converted into others in the process of their phylogenesis. The view expressed by Bernard (1951), that in the evolutionary history of the Hymenoptera the role of the behaviour factor was far greater than in the history of the other orders of insects, is therefore perfectly natural. However, as Brues (1946) has pointed out, the scientific investigation of this whole problem is still only fragmentary and far from adequate.