A Solitary Bee..The smallest solitary bees are 3-4mm long, the largest are about 15mm. This one was about 12mm.
Solitary bees are difficult to describe as there are many species that vary widely in their appearance. Some resemble small honeybees, others small bumblebees, while others could be mistaken for small wasps. Solitary bees differ from honeybees and bumblebees in not being social insects. A female solitary bee constructs and provisions her nest without the assistance of any worker bees. Despite this some solitary bees can be gregarious, with many bees making their nests in close proximity in a suitable piece of habitat.
Some solitary bees act like cuckoos, in that they are unable to make their own nests and instead enter the nest of another suitable host bee and lay their eggs there. When the cuckoo bee’s eggs hatch, the larvae make use of the nectar and pollen food store provided by the host bee.