One is the magic number

Back Garden Biology takes a closer look at the insects in the garden including the solitary bee. Solitary bees don't live in colonies and don't have a worker caste. Instead, the females must do the hard work themselves and rear their own offspring. Mining bees often dig holes in lawns and excavate burrows in which to deposit balls of pollen on which their larvae will feed. Mason bees and leaf-cutter bees do much the same, but use holes in walls, or bee hotels, provided by friendly gardeners. But, there are plenty of other insects happy to take advantage of their activities - many of them carefully disguised.