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In Utah, queens emerge from early April to May, the first brood emerges late June to early July, and overwintering queens cease activity in mid to late August. Second brood individuals are seen until early October (Nye, 1980). More northern populations have not been extensively studied.

Halictus farinosus belongs to the bee family Halictidae, which is characterized in part by a well-developed stigma, a single subantennal suture, and the first flagellar segment being much shorter than the scape. The genus Halictus is differentiated from other genera by strong, opaque apical wing veins, and, typically, apical hair bands across the abdominal segments. Halictus farinosus is the largest northwestern halictid bee, with females reaching up to 15 mm and males to 14 mm (Roberts, 1973; Ascher & Pickering, 2019). Females resemble those of Halictus rubicundus and Halictus virgatellus, but can be distinguished by the large size, broad apical fasciae on the metasoma, and hind basitarsus spur with small, regular-sized “teeth” (contrast to the spur of H. rubicundus). Males can resemble Halictus ligatus and H. rubicundus but can be distinguished by the short appressed hairs on the posterior margins of the fourth metasomal sternite (Roberts, 1973). Both sexes have no metallic tints to the body.

Halictus farinosus has a two-phase life cycle with social colonies, and is not known to be socially polymorphic like its close relative, H. rubicundus (Eickwort et al., 1996; Richards et al., 2010; Schwarz et al., 2007). It is suggested, however, that it may exist in solitary populations at more northern or high-altitude environments where the species’ behaviour has not been well examined (Richards & Packer, 1996). It resembles social populations of H. rubicundus in nesting behavior and nesting biology, such as brood size, nest architecture, and level of cast size dimorphism (Soucy, 2002). Halictus farinosus also resembles the appearance and behavior of Halictus parallelus, but H. farinosus is found in western parts of North America (Roberts, 1973). Nests are founded in the spring by previously inseminated immature queens that emerge after overwintering; these are known as foundress females or queens (Roberts, 1973). The nests are comprised of a horizontal main burrow that is excavated to produce a dirt mound outside the nest entrance, known as a tumulus. Tumuli symmetry can indicate interspecific differences; H. farinosus has a tumulus that is bilaterally symmetrical around the burrow entrance (Roberts, 1973). Foundress queens locate nests between April to May, going on to produce a first worker brood, followed by a second reproductive brood. The first brood is positioned higher in the nest and produces worker females; the second brood produces both males and females. Second brood females will be either gynes or non-gynes; gynes mate to later become new foundresses. Non-gynes do not mate and act as workers for the foundress queen. From being laid, the immature stages take approximately 25-30 days to develop. The males emerge in late summer, leave the nests, and do not return; at night, they sleeping on flowers and breed during the day. Brood cell size, egg development time, adult size, and caste size vary based on the season and soil temperature. All foundress females and males die before winter, while gynes overwinter and continue the cycle in the following spring (Roberts, 1973).

Halictus farinosus is a generalist polylectic bee known to visit many flower types, and has been observed foraging on 43 plant species from 14 families. Foraging trips usually last over an hour, but the bees will not forage in poor weather conditions such as heavy rain, strong winds, or cool temperatures.