Univoltine, with an extended flight period. Females fly from mid April to mid October; males from early July to the beginning of October.
Parasites and predators Sphecodes hyalinatus is a cleptoparasite of this species (R.C.L. Perkins, 1923, 1945). On the continent, Sphecodes crassus is cited as a possible cleptoparasite of this species (Söderman & Leinonen, 2003)
Systematics Formerly recorded in the British literature as Halictus subfasciatus Nylander (e.g. E. Saunders, 1896a), a name which embraced two species, Lasioglossum fratellum and L. fulvicorne. The confusion was eventually settled by E. Saunders (1904b), who recognised that both these species constituted the complex and the name H. subfasciatus was a misidentification. Both sexes of L. fratellum are easily confused with L. fulvicorne, the two forming a mainly allopatric species-pair.