amily of the order Hymenoptera consisting of small (> 4 mm) to midsize (> 8 mm) bees which are usually dark-colored and often metallic in appearance. Several species are all or partly green and a few are red (Figure 49); a number of them have yellow markings, especially the males, which commonly possess yellow faces, a pattern widespread among the various families of bees. They are commonly referred to as sweat bees (especially the smaller species), as they are often attracted to perspiration; when pinched, females can give a minor sting.
Common Sweat Bee. Image Courtesy of Jon Sullivan
Most halictids nest in the ground, though a few nest in wood. They mass-provision their young by providing a mass of pollen and nectar formed inside a waterproof cell. Once an egg is deposited on this mass the cell is sealed off. Thus the larva is with all the food at one time that it needs for full development, as opposed to "progressive provisioning", where a larva is fed repeatedly as it grows, as in honey bees. All adult species are pollen feeders and may be important pollinators. Several genera and species of halictids are cleptoparasites of other bees (mostly other halictids). The most well-known and common are species in the genus Sphecodes, where the female enters the cell with the provision mass, eats the host egg, and lays an egg of her own in its place.
Halictidae are one of the four bee families that contain some species that are crepuscular. These bees are active only at dusk or in the early evening or sometimes truly nocturnal. In these cases they have greatly enlarged ocelli or simple eyes to enhance their night vision.
Megachilidae-Leaf Cutting Bees and Mason Bees. The Megachilidae are a cosmopolitan family of solitary bees (Figure 50) whose pollen-carrying structure (called a scopa) is restricted to the ventral surface of the abdomen (rather than mostly or exclusively on the hind legs as in other bee families).
Leaf Cutting Bee with Pollen Trapped on Underside of Abdomen.
Megachilid genera are most commonly known as mason bees and leafcutter bees, reflecting the materials they build their nest cells from (soil or leaves, respectively); a few collect plant or animal hairs and fibers, and are called carder bees. All species feed on nectar and pollen, but a few are cleptoparasites (informally called "cuckoo bees"), feeding on pollen collected by other megachilid bees. These parasitic species do not possess scopa and are incapable of collecting their own pollen. The brightly colored scopa leads to a colloquial name used occasionally in North America - "Jelly-belly bees." Megachilid bees are among the world's most efficient pollinators because of their energetic swimming-like motion in the reproductive structures of flowers, which moves pollen, as needed for pollination. One of the reasons they are efficient pollinators is their frequency of visiting to plants. In actuality they are extremely inefficient at gathering pollen when compared to all other bee families. However, megachilids require on average nearly ten times as many trips to flowers to gather sufficient resources to provision a single brood cell. Of course with more, more pollination is accomplished.
North America has many native megachilid species, but Alfalfa leafcutter bees (Megachile rotundata) are an imported species used for pollination. The most significant native species is Osmia lignaria (the "Orchard Mason Bee" or "Blue Orchard Bee"), which is sold commercially for use in orchard crop pollination, and which can be attracted to nest in wooden blocks with holes drilled in them (which are also sold commercially for this purpose).
Leafcutter bees nest in soft, rotted wood; thick-stemmed, pithy plants (e.g., rose); and in similar materials that the bees can easily cut through and excavate. Nest tunnels may extend several inches deep and coarse sawdust may be deposited at the entrance. This sometimes causes confusion with other wood nesting insects such as carpenter ants. However, leafcutter bees restrict their tunneling to soft, rotted wood and do not cause da