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The genus Agapostemon is a common group of Western Hemisphere sweat bees of generally green or blue appearance (head and thorax almost always, sometimes also the abdomen in females, most males have the abdomen yellow banded on a black or metallic background). Some 42 species are in the genus, which ranges from Canada to Argentina. They superficially resemble various members of the tribe Augochlorini, which are typically metallic greenish in appearance. All species nest in the ground, sometimes in dense aggregations. Some species are communal, i.e. multiple females share the same nest entrance but beneath the common entrance burrow construct their own portion of the nest, dig their own brood cells and collect pollen and nectar to fashion the pollen ball upon which they will lay an egg. Unlike many other social bees, there is no reproductive division of labour. The advantage of this form of sociality seems to be that cleptoparasitic 'Nomada' bees have greater difficulty gaining access to the nest and brood cells when there are multiple females inside. In cool temperate regions at least, there is one generation a year with females being active in early summer and males and pre-diapausing females active in late summer. Only mated females survive the winter. Males can often be seen in large numbers flying around shrubs with large flowers, such as rose of sharon.