The Cylindropuntia cactus at the 30th St Greenhouse is a real magnet for Lithurgopsis apicalis, a cactus specialist! Notice the tubercles (tiny horns) on top of her head! There were dozens of females visiting flowers and foraging for pollen. I had seen these on Opuntia while out on the plains, but the Cylindropuntia is from the southwest. Apparently, our Opuntia specialist likes it too!
I am a Postdoctoral Associate at CU-Boulder and have lead a number of projects studying patterns of native bee diversity in Colorado. Please enjoy your visit and contact me if you have any questions.