PHORESY among arthropods has been widely noted and its importance in population dispersal and survival appreciated. Hypopi, the phoretic stage of mites, have been studied for the most part isolated from their hosts, and little is therefore known of their interaction. We have recently described some behavioural adaptations of the hypopus of Myianoetus muscarum (Anoetidae) to fly factors which favour the mite's dispersal1. Hypopi are attracted to a volatile substance produced by the pupae of several fly species, including Musca domestica, Muscina stabulans and Stomoxys calcitrans, and cluster on the anterior end of the pupal case from which the fly is due to emerge. This communication describes the behaviour of the same mite on adult M. stabulans.