Solitary bees.

The great majority of bees in Britain do not live in organised colonies like honey-bees and bumble-bees. They are solitary insects that make small nests in soil, hollow stems, decaying stumps or mortar. The female lays a few eggs in the hole and then moves on to build other nests. Once she has laid all her eggs she usually dies, leaving the nests stocked with food for the developing larvae to eat. Some species build their nests close together and then guard the entrances from predators, such as cuckoo bees which may try to take over the nests and lay their own eggs in them. Britain has 227 species of solitary bees, compared to only one species of honey-bee. Many solitary bees  look like honey-bees in shape and colour but are usually smaller. They do not have a worker caste- just males and females. They are dependent on flowers for food and are a major force in pollinating plants.