Megachile rotundata, the alfalfa leafcutting bee, is a European bee that has been introduced to various regions around the world. As a solitary bee species, it does not build colonies or store honey, but is a very efficient pollinator of alfalfa, carrots, other vegetables, and some fruits. Because of this, farmers often use M. rotundata as a pollination aid by distributing M. rotundata prepupae around their crops. Each female constructs and provisions her own nest, which is built in old trees or log tunnels. Being a leafcutter bee, these nests are lined with cut leaves. These bees feed on pollen and nectar and display sexual dimorphism. This species has been known to bite and sting, but it poses no overall danger unless it is threatened or harmed, and its sting has been described as half as painful as a honey bee's. Taxonomy and phylogeny M. rotundata is a member of the subfamily Megachilinae, which includes more than 4,000 bee species; this currently makes this family the second-largest among all bee families. This subfamily is one of four other subfamilies of Megachilidae, the other three being the Fideliinae, Pararhophitinae, and Lithurginae. Phylogenetic studies suggest that this subfamily is monophyletic. More specifically, it belongs to the genus Megachile, which contains 52 subgenera and 1,478 species. The genus Megachile consists of bees that cut leaf pieces to line their nests. Description and identification M. rotundata is a European leaf-cutting bee placed in the subgenus Eutricharia, the "small leaf-cutting bees"; they are in length. They are partially bivoltine, meaning that under the right conditions they can produce two generations per year. These bees present a sexual dimorphism, in which the males are smaller than the females and differently marked. M. rotundata bees are a dark grey color. Females have white hairs all over their bodies, including on their scopae. In contrast, males have white and yellow spots on their abdomens. Distribution and habitat M. rotundata is currently found on all continents except Antarctica. In North America, the species was deliberately imported to assist in the pollination of food crops, but has now become feral and widespread. In New Zealand and Australia, M. rotundata was also introduced to assist in the pollination of alfalfa (known locally as lucerne), in 1971 in New Zealand, and 1987 in Australia. Nest construction Females construct tubular nests in a variety of sites, including rotting wood, flower stems, reeds, and