There are 77 species of Solitary bee resident in Ireland and all are excellent pollinators. They do not live in colonies like honeybees or bumblebees. Instead of egg-laying queens in hives solitary bees have females that mate, lay eggs and build nurseries.
If you erect a solitary bee nursery like the one in the picture facing South or South-East and at least a metre from the ground, you may attract the Mason bees (Megachile spp.) or the Leafcutter bees (Megachile spp.) (1) The entrance holes to the cavities should be without splinters and between 2mm and 10mm in diameter to cater for different species. These bees collect pollen and nectar and leave little cakes of this mixture in the cavities for their larvae. They then deposit an egg on each cake. Leafcutter bees seal each chamber and the entrance with a piece of leaf. (Look at rose leaves and you will often see little discs cut out by these bees). (2) Mason bees seal each chamber and entrance with mud. (3) When the eggs hatch the grubs eat the pollen and nectar. (4) After a number of days, they turn into pupae and remain thus over winter before emerging in spring. Males coming first so as not to interbreed with the females.
These solitary bee nurseries are often called bee or bug hotels, but they are not hotels and they do not cater for bugs. (“Bug” is a term often applied to insects and other invertebrates in general. A bug, however, is only one kind of insect-one with a sucking mouthpart). This box is for rearing young bees. It should be brought into a cool, dry shed in October to keep it dry and re-positioned in March. They should be cleaned regularly after use.
Mining bees (Andrena spp.), the commonest species of solitary bee in Ireland do not use nursery boxes. They excavate tunnels in sunny banks of sand or soil in May in which the females lay eggs in food-laden cells (4) like the ones already mentioned. These will emerge to produce broods of their own in July.