Carpenter bee heading for flowers of the native "climbing bush penstemon" (Keckiella cordifolia).

Note the long red flowers here are of the type commonly associated with hummingbird pollination. Red is supposedly more visible and attractive to hummingbirds than to bees, and the placement of the anthers far out at the end of long stamens would suggest this flower is well-suited for depositing pollen on the top or bottom of a hummingbird's head or body. It seems the corolla tube may be too long and thin for the nectar at its base to be effectively accessible to this carpenter bee. But caution!...I've read that these types of presumptions & generalizations are often in error...more the product of speculation than rigorously verified empirical observation and quantitative analysis. Often many disparate pollinators may be involved with a given plant and, without careful study, it may not be clear which is the most frequent and/or effective at transferring pollen and promoting successful cross-fertilization. (I don't know for sure here...so indeed my comments are, strictly speaking, speculation!)

However, as the images in the series show, this carpenter bee did proceed to "nectar rob" by biting a hole at the base of the corolla, rather than entering at the throat of the flower, as would a "legitimate pollinator". So perhaps its large size and an insufficient tongue-length do indeed deter or prevent it from reaching the nectar via the "legitimate" approach. As an interesting contrast, this was not the case in the posts of the Xylocopa tabaniformis ssp. orpifex seen here...visiting the shorter-tubed, white flowers of the congener "gaping bush penstemon" (Keckiella breviflora) in mountains to the north of the locale here.

As far as ID goes, from my reading of the info in "The Carpenter Bees of California" (by P. Hurd, 1955, available as a PDF here), I'm thinking this is either Xylocopa tabaniformis ssp. orpifex or X. californica ssp. diamesa. And since the metasoma seems mostly black (rather than metallic blue), I'm guessing it's X. t. orpifex. I'm also thinking it's a female since, as best I could count, there are 6 visible metasomal terga...as opposed to 7 for males (see the 4th image in this series). But I'm definitely hoping Dr. John Ascher will correct (or possibly confirm?:-) my interpretations here.