Carpenter bees in the genus Xylocopa are widely distributed and quite large solitary bees.   They get their name from the neat, round nesting tunnels females drill into wood, including houses, decks, or other structures.   The carpenter bee shown here is either the Valley carpenter bee X. varipuncta or the California carpenter bee X. californica; both are very common in the southwestern US.   Females, like these, are shiny black, while the less frequently seen males are a bright buffy or rusty color.   These bees have a powerful sting but are very reluctant to use it.   I took these pictures as the bees fed in (and pollinated) the large white blossoms of a cactus, Echinopsis (Trichocereus) candicans.   The following day, all of the 50+ flowers on this briefly-blooming plant had closed.