Mason Bees

Mason, blue orchard or Metallic leafcutter bees, Osmia are very competent pollinators. One of the Cherry Orchards in Utah found a 300% increase in yield when they switched from European honey bees to Blue Orchard Bees (in How to Manage the Blue Orchard Bee by Bosch and Kemp). These little buzzers are about half the size of Honey bees but their brain seems bigger and they'll work the flowers on cloudy days and earlier in the morning and later in the evening. They build their nests in cracks in rocks, mud or woody material.They plug the nest entrance hole with leaves and then with mud.
Mason bees do have stingers but only use them to defend themselves from things like dumb human hands squishing them.
If you have a garden or an orchard and want to attract these little bees, plant some early-season flowering plants Arctostaphylos glauca or 'Austin Griffin' manzanitas to provide food for them before your crop flowers, and some late-season flowering plants, Salvias to provide food for them, when hardly any crop plants are flowering. This way you can build up their population, and keep them alive and thriving all year round, and they will repay your effort by helping to increase your crop yields in your garden or orchard.

Mason, blue orchard or Metallic leafcutter bees, Osmia come in many flavors and colors.