Solitary bees in Britain are highly diverse, and so are their nesting habits. Each species has very particular requirements but the majority excavate their own nest tunnel in the ground.
The female builds the nest by herself, choosing a suitable piece of ground and using her body to dig out a nesting chamber. She adds pollen to the chamber, which is often moistened with nectar, and lays an egg. She then seals off that section of the nest before moving onto the next chamber. Although most solitary bees make solitary nests, in suitable nest sites you often find aggregations of nests. Some ground-nesting species also create turrets over their nests, and these are often very distinctive.
A number of species nest aerially, usually in old beetle holes and often sealing the nests with a saliva like substance, mud, chewed leaves, resin or sections of leaves which they cut with their jaws. These species are the ones most likely to take to artificial nests in gardens.
Finally, there are three British species that nest inside snail shells. They use chewed up leaves to seal off each section within the empty shell, and often camouflage the shell in some way.