A univoltine species; late May to the end of July, and sometimes into August at higher altitudes (Edwards & Else, 2018; Amiet et al., 2004). Bossert (2014) records flight activity in June in the Austrian Tyrol
Parasites and predators The chrysidid wasp Chrysura hirsuta as been reared on several occasions from Scottish nests of this species (e.g. Evans, 1899b; Else & Edwards, 1996). The larva of this cleptoparasite attacks the host larva after the latter has spun its tough reddish-brown cocoon. When fully fed the C. hirsuta larva spins its own cocoon within that of the host (see illustration in Morgan, 1984). The chrysidid also seems to have an obligate,minimum, two-year life cycle which parallels that of its host.
In Sweden, the sapygid wasp Sapyga similis (a species not recorded from Britain), an ichneumonid wasp in the genus Hoplocryptus (B. Svensson, pers. comm.), and the chalcid Pteromalus osmiae (Hedqvist, 1979) have also been reared from Osmia inermis cells.