One of the most charming natural history writers, in the original French, or translated into English, is Henri Fabre. He was particularly fascinated by the bee genus Osmia, known as Orchard Bees or Mason Bees. His observations and notes on this group in particular set the standard for modern natural history and ecological research. You can read him (translated into English) on Osmia at efabre.net, a wonderful resource. Without his careful and lengthy investigation of their lifecycle and behaviour we would know far less about these bees. As it is, he describes many species, how they build nests, what ratio of males to females emerge, and all manner of delightful nuggets of information.
Note the white face and long antennae.
Males cannot sting, and females, although they have a sting, it is smaller than a honey bee's and they rarely use it. They are closely related to the Leaf-cutter bees, and like them, carry their pollen load under their belly, not on their hind legs like honey bees and bumble bees. They will happily nest in man made nesting tubes, such as bundles of hollow canes or blocks of wood with holes drilled in them. The holes need to be about 8mm in diameter and 10 - 25 cm deep.
Note: The natural distribution of Osmia cornuta is across central and southern Europe. The species does not occur in Britain, so if you are seeing a black and red bee in early spring it will be the Red Mason Bee O. rufa or more likely, the Tawny Mining Bee Andrena fulva.