I felt lucky to capture a shot of this black-and-white bee, if only from the back. It turned out to be a plasterer bee (family Colletidae).
This mostly solitary bee is often only active for a few weeks each year. The female gathers pollen in a ball, places an egg on it and hides it in a burrow that she "plasters" with a special secretion. The secretion dries like cellophane and makes the burrow waterproof. The young bees eat the pollen and stay in the burrow over the winter, emerging in the spring as adults. Kind of a boring life, but it works! And they pollinate flowers along the way.
Another bee cousin is the bumble bee:
Bumble bees build colonies, too, but the hives are smaller (sometimes just 50 bees or so) and not nearly as well-organized. Bumble bees can also sting but rarely do so. I was chasing this gal all over trying to get a good shot.
I took it in the garden of the man who's responsible for the plant collections at the Denver Botanic Gardens. His place overlooks Denver from the east (if it weren't cloudy, you could see the mountains) and is a great example of turning an awkward blank slate of a yard into a showpiece. I'm taking notes!