A univoltine species flying From May to June inIberia and as early as March in the Maghreb (Müller, 2018)
Parasites: In Spain, the cleptoparasitic bee Stelis odontopyga was found at the same localities as Osmia fallax inhabiting empty snail shells (Moreno-Rueda et al. 2008), suggesting that Stelis odontopyga, which is known to be a cleptoparasite of Osmia spinulosa, might also parasitize Osmia fallax (Müller, 2018)