Larval water mites of the genus Arrenurus, ectoparasitic on zygopteran imagine of Enallagma cyathigerum, contact the aquatic zygopteran nymph and cling to it, awaiting the emergence of the zygopteran imago. Thus the phoretic association of the water mite with the nymph is established prior to the parasitic phase. Ultrastructural evidence indicated that the phoretic larva sticks to its potential host by means of an adhesive substance deposited between the larval pedipalps and cuticle of the zygopteran nymph. The adhesive substance appears to be secreted by the arrenurid larva.