Bees create a buzz
Entomologist Chris O’Toole discusses the diversity of our native bees, the threats they face and what we can do to help.
On a global level, every third mouthful of human food is directly or indirectly dependent on the pollination services of bees. These insects are thus a vital natural resource and are well worthy of study and conservation.
Everyone is familiar with the honeybee and the brightly coloured, fluffy bumblebees. These are social species and live in organised colonies comprising a dominant egg-laying queen and a large number of sterile females or workers and a smaller number of males; in Britain, there are 23 different bumblebees.
But the vast majority of the 254 species of bee native to Britain are solitary or non-social: each nest is the work of a single female operating alone and there is no caste of collaborating workers. Unlike the honeybee and the bumblebees, the solitaries do not make and store honey: they are largely pollen driven. The majority are called mining bees because they excavate their nests in the ground. Most mining bees prefer dry, well-drained light or sandy soils, though some prefer near-vertical clay banks and all construct cells which they line with a glandular secretion which is waterproof and resistant to fungal attack. In each cell the female stores pollen moistened with a little nectar and lays a single egg.
The other large group of solitary bees are the masons, leafcutters and the carder bees. These have two things in common: the females carry pollen in a modified brush of hairs on the underside of the abdomen rather than on the hind legs and, instead of excavating nests in the ground, they use pre-existing cavities such as beetle borings in dead wood or hollow plant stems. Two species of mason bee are ultra-specialists: they nest exclusively in empty snail shells.
These cavity-nesting solitary bees differ from the mining bees in that they do not line their cells with glandular secretions. Instead, they gather materials from the environment to use as building materials: according to species, mason bees use either mud or a mastic of chewed leaves, while leaf-cutter bees use pieces of leaf excised from the margins of leaves. The carder bee is so-called because is teases out or ‘cards’ the downy hairs from the leaves of certain plants.
This diversity of bees is under threat from intensive agriculture, which has brought about widespread losses in floral diversity and the destruction of nest sites; much of our modern agricultural landscape is no longer very bee friendly, with the result that 25 per cent of our native bees are on the Red Data Book list of endangered species.
Domestic gardens, with their contrived floral diversity, are havens for our native bees. We can help their conservation by not planting double-flowered varieties in which pollen and nectar producing structures have been lost. Just as we can put nest boxes out to attract birds, we can now to do the same for mason bees. The Red Mason, Osmia rufa, visits a wide range of garden flowers and is an highly efficient pollinator of fruit trees, especially apples, pears, plums and cherries; it is active from late March to mid-July. At least two species of leaf-cutter bees (Megachile spp.) will also use the nests and nests are also available for another useful pollinator, the Blue Mason Bee, Osmia coerulescens.
None of these bees make and store honey, so they do not have a large, calorie rich resource to defend. As a result, they are very docile and are quite safe with children and pets.