Sizes range from five millimeters to on inch. They are dark in color with several whitish hair bands across the abdomen. Pollen is carried exclusively on the underside of the abdomen, never on the hind legs. Nests are in hollow twigs, stalks, holes in logs, in dried rolled-up leaves, or in the ground. Megachile species cut leaf and flower pieces from preferred plants and use them to build capsulelike cells.
Several species are important pollinators of sunflowers.
The alfalfa leafcutter bee, the smallest, was introduced from Europe and is often propagated for alfalfa pollination. The single Missouri species prefers coniferous wood and often reuses old nests, cleaning them of debris and enlarging them. Structural damage to timber can result from many nests. Carpenter bee nests are provisioned in the spring and summer. After emerging, the young adults fly and feed briefly before overwintering in the tunnels.