Alfalfa leafcutter bees (Megachile rotundata) are so named because the bees make their nests from circular disks cut from plant leaves, often from the alfalfa plant (Medicago sativa), by the bees' mandibles. This bee is native to Eurasia, but was introduced to North America sometime after the 1930's; it is now feral and widespread in the United States and northern Canada. Alfalfa leafcutter bees are 1/4 to 3/8 of an inch long. They are black with whitish or yellowish bands on their abdomens. Alfalfa leafcutter bees have been used as commercial pollinators of alfalfa for over 50 years. They also pollinate carrot (Daucus carota), onion (Allium spp.), and wild blueberry (Vaccinium spp.) crops as well as sweet clovers (Melilotus spp.), white clover (Trifolium repens), and some wild mints (Mentha spp.). Stiff hairs on the bee's abdomen collect pollen during foraging. This pollen is then inadvertently transferred to other flowers while the bee continues to forage.

Several factors make the alfalfa leafcutter bee a good commercial pollinator. These bees are easy to manage, requiring only moderate time and money, and are non-aggressive. Although they are solitary nesters, they are gregarious so females nest in groups and they can be induced to nest in artificial nesting sites like drinking straws or drilled blocks of wood. These bees are easily transported during the immature stage and colony size grows rapidly. Additionally, they forage close to their nest sites, usually within a few hundred feet of the nest, and will remain primarily in the field to which they are supplied. Finally, they have a long field life of up to nine weeks.