Dang, Michael Bush has a lot of black bees. Mystery solved!
Since I started keeping bees, I am more observant of them. For several months I have seen an occasional very small black bee foraging about the ranch. I assumed they were was another species of bee, but then a few weeks back I saw one go into one of my hives. The next time I did an inspection I looked carefully and saw a few of the small black bees. The queen of this hive is a small bee that is mostly black, but she does have some very faint yellow streaking. The genetic makeup of bees is too complicated for this old engineer, but apparently the breeding process of queen bees produces many strange variants.
As the youngsters say, bees are "cool."