The genus Vidia Oudemans is reviewed and four new Nearctic species described: V. rubi from all ontogenetic stages associated with Megachile rubi, V. latimanus from deutonymphs from M. latimanus, V. hirsuta from deutonymphs from M. fidelis, and V. texanafrom deutonymphs from M. texana. Based largely on observations of V. rubi, po st-deutonymphal instars of Vidia occur on the leaves that Megachile bees use for nest cell walls, where the mites presumably feed on fungi. They do not occur on the bees provision masses nor on the young bee larvae. The ontogeny of V. rubi is discussed in a phylogenetic context. The genus Vidia is redefined and its systematic position as sister-group to the remaining genera of the subfamily Ensliniellinae is hypothesized based on cladistic analysis.