an increase their attractiveness to bees by drilling nesting holes following the size recommendations listed above for wood blocks.
Adobe blocks can also be easily made where clay soils are common. To create one, half-fill a large bucket with clay soil, and then fill the bucket with water. Stir the mixture together to create muddy slurry and allow it to settle. Remove any sticks or debris floating on the surface and slowly pour off most of the water. Finally, pour the remaining sediment into a mold (such as a wooden box or small Styrofoam cooler), and allow it to dry for several days or weeks. Before it completely dries, you can make several 1-inch indentations, using the diameter guidelines above, to make it more attractive to bees.
Mount the brick, either singularly or in a stack. Adobe will not hold up well in wet climates and many need sheltering from rain. You might want to supply a shallow water source near your bricks to help bees excavate their nests.
Halictidae-Halictid Bees. This is a cosmopolitan family 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 s