Here it's cutting off part of a petal. It finished off by spinning
like a dervish to separate the piece. They are solitary bees and
after mating the female does all the work. She burrows a tunnel in soft
earth or plant pith which she lines with leaf (and petal) cuttings. Then
she lays eggs and wraps each one along with some pollen for its first meal
leaving them to develop on their own.
In Colorado, they are used as very efficient pollinators of alfalfa...
better than commercial honeybees. Pre-drilled nest boards are placed
in the fields to encourage their presence.