Cactus Bees are solitary, ground-nesting bees that specialize on the flowers of various kinds of cacti. The photos below show a Cactus Bee buried deep inside a Calico Cactus flower. There are some 23 species of Cactus Bees in the U.S. Southwest, and they serve as major pollinators of these plants. They alight first on the flared, over-size, green stigma that is borne above the stamens - thus depositing some grains of pollen from the last visited flower. Finally they push down through the forest of stamens to get at the nectar deep inside. Their hairy bodies gather more pollen and their long tongues lap the nectar. Both are carted back to their nests in the ground which they build and provision solitarily, i.e. they do not live in hives. The photos below are from a recent Desert Sampler Tour.