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.