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Halictus rubicundus 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. Females of H. rubicundus usually have a narrow cleft on tergite five, and males are sometimes without apical hair bands. Both sexes have no metallic tints to the body, and are approximately 10 to 11 mm in length. Females can be distinguished from females of Halictus farinosus by the narrow apical fasciae bands (Figures 1-2). and an inner spur on the basitarsus of the hind leg that has “teeth” of irregular size (Figure 3). Females can also resemble Halictus virgatellus, but are larger in size and have a shorter cheek length (Roberts, 1973). Males of this species can be differentiated from other males of the Halictus genus by the abundant hairs on the posterior margins of the fourth metasomal sternum (Roberts, 1973).

Halictus rubicundus has been studied extensively for its ability to exhibit social plasticity based on its climate. Typically, cooler, high elevation habitats are where it remains solitary. In warmer, longer season habitats, it often becomes eusocial. There is some evidence of social inflexibility, however, as it sometimes remains social even at high altitudes (Eickwort et al., 1996). The nests are haplometric and the females are generally philopatric, returning to the same nesting areas (Yanega, 1990). 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 vertical 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. rubicundus has a tumulus that is radially symmetrical around the burrow entrance (Roberts, 1973). The annual colony cycle differs between social or solitary populations; solitary populations have one brood and a higher percent of females that mate before hibernation, and social populations can have more than one brood with later broods having a higher percent of males (Soro et al., 2010; Soucy, 2002). Broods emerge in June, and in social populations the first brood females will act as workers for the foundress queen female who continues to lay eggs, and some later mate before hibernation in the winter. (Soucy, 2002). Non-gynes do not mate and act as workers for the foundress queen (Yanega, 1989). The males emerge in late summer, leave the nests and do not return; at night, they sleeping on flowers and copulate during the day. Brood cell size, egg development time, adult size, and caste size vary based on the season and soil temperature.

This species is a generalist polylectic pollinator that feeds on nectar and pollen from a variety of flowering plants, and may be important pollinators due to their abundance in North America (Roberts, 1973). The bees will not forage in poor weather conditions such as heavy rain, strong winds, or cool temperatures.