KEEPING; SOCIAL INSECTS). Solitary bees nest in a variety of situations : many, such as Andrena and Halictus, construct burrows in the ground with the individual cells leading off from the main passage.
Others, such as Osmia, utilise existing hol lows or crevices whether they be in wood, bramble-stems or mortar : they may even occupy empty snail-shells or key-holes.
About to to 20 cells usually compose a nest, but one of 230 cells is recorded. The mason bee (Chalicodoma) of southern Europe builds its nest often on large stones : the individual cells are constructed of soil and small pebbles mixed with saliva and the whole nest is plastered over with the same material until it assumes a dome-shaped form, about the size of half an orange. The carpenter bees of the genus X ylocopa include the largest of all bees and are chiefly found in warm countries. although one species occurs as far north as Paris. These giant bees tunnel by means of their powerful jaws in dry wood for a distance of a foot or more, dividing their burrows into a series of cells formed of agglutinated wood particles. The genus Megacliile includes the leaf-cutting bees which nest in soil, in wood, or in hollow stems. The cells are thimble-like in form and constructed of rounded pieces of leaves or petals which are cut by the jaws of the bee from roses and other plants : the more ovoid pieces form the bottoms and side-walls of the cells; these are closed by several circular pieces which are firmly pressed down to form closely fitting lids. (See SOCIAL INSECTS.) A number of solitary bees construct no nests of their own but live as inquilines or "cuckoo-parasites" in those of other species : such bees are less hairy than usual and lack special modifications for pollen-collecting. The black and yellow species of Nomada lay their eggs in nests of Andrena, and their larvae are nourished at the expense of those of the latter, which become starved out. Another parasitic bee, Stelis, utilises a species of Osmia as its host : its eggs are laid earlier than those of the Osmia and are placed towards the bottom of the food-mass in the cells, whereas the eggs of the host are laid upon the surface of the food. Both larvae feed amicably at first but finally the Stelis larva attacks and devours that of the Osmia.
interesting observations on the habits of solitary bees will be found in J. H. Fabre, Souvenirs Entomologiques (1879-9i) and C. Ferton, La Vie des Abeilles et des Gilepes (1923) . A very readable account of the chief European species is given by H. Friese, Die Europiiischen Bienen (1923) and the British species are described and figured by E. Saunders, The Hymenoptera Aculeata of the British Islands (i896). (A. D. I.)