During the last few decades, a considerable amount of experimental works has been carried out on the relations of insects to their environment: in certain groups such studies have advanced to an extent which renders possible tentative efforts at accurate prediction of their activities and spread. Among the arachnids, however, the experimental study of ecological relationships has been almost entirely neglected, and this despite the fact that several species, especially among the mites and ticks, are of marked economic significance. Since 1892–3, when the researches of Smith and Kilborne on piroplasmosis in cattle were published, ticks have been proved to be vectors of numerous important diseases of man and animals in many parts of the world, and much knowledge of their bionomics has been gained through observations conducted in the field and in the laboratory. The ecology of ticks under precisely controlled conditions, however, provides a practically unexplored field.