My wife organized a group of naturalists to visit "Emerald Valley" on the back side of Cheyenne Mountain, beyond the reach of The Broadmoor resort camp, on June 29. A break from the mostly overcast and rainy weather we've been having allowed us to observe several species of bees. Even the trail itself provides bare earth that burrowing bees like to nest in.
Sometimes, you are what attracts bees. I had the pleasure of entertaining a female "sweat bee," genus Halictus, as she sipped my perspiration during the Emerald Valley trip.
Bees do have their enemies, and sometimes those enemies are other bees. I was stumped by one particularly large, solitary bee I encountered on May 28 in Cheyenne Mountain State Park. The insect landed on the trail and stayed there, allowing me to approach close enough to take pictures. Doug Yanega of the University of California, Riverside, another top-notch bee expert, kindly provided the identification of Melecta pacifica fulvida. It turns out this species is a cleptoparasite of the digger bee Anthophora pacifica. The female Melecta enters the burrow of its host and lays an egg there. The larva that hatches then eats (steals) the pollen and nectar intended for the host's offspring.
Source: Scott, Virginia, John S. Ascher, Terry Griswold, and César R. Nufio. 2011. The Bees of Colorado. Natural History Inventory of Colorado No. 23. 112 pp. (PDF version)..