Small bee on crocus

Nice sunny day (18 degrees by the thermometer on the rockery). I noticed a small bee visting the crocus on the rockery. It looked like a honey bee but appeared much too small so suspected it might be one of the solitary bees.

However, after sending the picture for advise, I found out that honey bee workers vary in size according to how big the cell in the honey comb is that the egg was laid in. As the years go by, with the cell used over and over again to to rear bees the cell walls thicken and the cell gets smaller inside.