I would go for Solitary Bees, you do get mason or mortar bees but they tend to like walls and as name suggests, mortar.

I get loads of Solitary bees in my grass and between the patio paving, talk about long time cutting the grass! Mind the bees! it takes me ages :-)
outside their holes (burrows) you will see little pile of fine earth- looks so very much like worm casts....but watch a while and you might see a bee! I love watching them come and go, and would love to see into their homes.

Found this, hope it helps

Solitary Bees (Burrowing Bees)

There are many species of bees which are solitary by nature, but the commonest group belongs to the genus Andrena and these are frequently called mining bees. They are rather variable as far as size and colour go, but are generally quite hairy and closely resemble the honeybee. They can be distinguished quite easily by their short tongues and the most constant feature is the marked flattening of the abdomen. One of the best known species is the tawny mining bee, Andrena fulva, which has its thorax and abdomen richly covered in dark tan coloured fur.

Each individual female bee will make a nest in a suitable position in the ground, usually selecting light sandy soil, domestic lawns being an ideal situation. There may be many individual nests grouped closely together, taking advantage of the ease of excavation of the light soil and giving the impression of communal living. Each female, however, is working alone to excavate a small burrow with perhaps half a dozen earthen chambers.

There is no contact between the parent and offspring, the female bee showing no interest in the progeny after she has created and provisioned the cell and she is probably dead before they emerge. Most of the species emerge from their nests in the spring and after mating the females start making new burrows. Many species produce a second generation about July time but others take a whole year to complete their life cycles and adults are only found for a short period during each year.

They sometimes cause a minor nuisance until they disappear in mid-summer but the use of insecticide is unnecessary, as they cannot successfully sting humans.

Enjoy your bees, if you can give them a little space and time that would be great!