SPECIES: nitidulus; COMMON NAME: Neon Cuckoo Bee
This is a black bee with metallic blue spots on the back and sides. They are called cuckoo bees as they lay their eggs in the burrows of other bees.
A relative of the Cuckoo bee is the Thyreus caeruleopunctatus. It has light blue patches on the back and sides. Otherwise its description is the same as for the Thyreus nitidulus.
I do quite often see solitary little blue bees in our garden and now wonder if it is one of the above.