Reports on life-cycles, parasitic associations and physiological properties of Parasitengona are reviewed and supplemented by unpublished data. The life-history pattern of the stem species of Parasitengona and Trombidia is reconstructed along the phylogenetic system. It is hypothesized that these stem species displayed an epigaeic life style in biotopes with fluctuating air humidity. Larval parasitism of Parasitengona on flying insects is directly derived from a predatory life-style, the main advantage being the increased ability to disperse via the host. Calyptostasis in proto- and tritonymphs evolved to ease synchronization of life cycles with optimal host availability. Protelean parasitism and evolution of calyptostatic instars led to restricted possibilities to increase offspring numbers. High larval mortality in turn led to a number of different pathways to circumvent this constraint, e.g. neosomy or additional moulting of postlarval instars. In the stem lineage of Hydrachnidia an aquatic life style evolved in temporary waters, Trombidioidea switched to an edaphic life in its stem lineage, while Erythraeoidea adapted to xeric environmental conditions. The causes of the diversity and success of parasitengone groups are discussed.