Probable Identification: Andrenid Bee [0141_alt]

What type of bee is this? Her abdomen was black, shiny, with black hairs. This is a 100% crop, unfortunately.

 

Her and her sisters were swarming my Hawthorne tree, which is currently bursting into bloom.

 

This is a metric measuring tape -- she's about 1.3cm long.

 

This image was on Flickr's Explore May 22, 2007, likely because of all the helpful people trying to ID it. :) Thanks!

Done