The 3 main groups of solitary bee found in Britain are mining bees that nest in underground burrows; and mason and leaf cutter bees, comprising over 150 species, that nest in small horizontal holes. Although some can sting they are unlikely to do so. These bees are important pollinators of our cultivated crops and wild flowers. Increasingly their natural habitats are being destroyed and these fascinating little creatures are under threat. Encouraging them into and protecting them in your garden is a very worthwhile step to help conserve these creatures and at the same time get great pleasure from observing them.
THERE ARE AROUND 250 SPECIES OF SOLITARY BEE IN THE UK
The most common mason bee in Britain is the Red Mason Bee Osmia rufa. The adults emerge in the spring. Males usually emerge first. They then wait eagerly for the females to emerge so that mating can take place. Once mated the female starts her search for a suitable nest hole.
The nest will be in any small cavity such as a crack in the wall, hollow plant stems, snail shells or even the
sunken screw holes in a garden table and chairs. Osmia rufa often nest in the mortar of old walls, enlarging cracks – their jaws are strong enough to attack mortar. They do not normally cause problems but weak or crumbling mortar may need attention to prevent further weathering.
The female is between 10 and 13 mm long and reddish brown in colour. She has a pair of “horns” on her face that she uses to tamp down mud when closing a brood cell. Males are often seen flying together in a zig-zag fashion a few centimetres above the ground searching for a female with which to mate.
On cold days bees need to warm up before they can fly and so females are often seen in the morning sunbathing by tunnel entrances. These bees are important pollinators of garden and wild flowers and should be encouraged and conserved. The adults are only active for between 6 and 8 weeks in the year.
LEAF CUTTING BEE
Gardeners often notice crescent shapes cut from the leaves of their rose bushes in early summer. This is
evidence of the activity of leaf-cutting bees. The most common species in the UK are Megachile centuncularis and Megachile willughbiella. They use the leaves of roses as well as those of willow herb, lilac and beech trees. Female bees are about 1 cm long, black in colour with conspicuous orange red fringes of hair, for carrying pollen, on the underside of their bodies.
They are active in the spring when mud, often mixed with saliva, is used to make the partitions between the cells in the nest tunnel, which is usually about 7 mm in diameter. Firstly a small pellet of pollen and nectar is placed in the tunnel. An egg is laid close to or on the pellet and the cell is closed off. The procedure is repeated and so a row of nest chambers, usually between 4 and 6 although sometimes 10 cells long, is completed. Great attention is paid to the final wall so that it will prevent other tubular cavity nesting species from utilizing the empty space. Four of five similar nests will be completed in a season.
There is one generation a year. The bees become adult in late September early October and remain inside their cocoons until the following spring.
Each spring little mounds of earth, rather like worm casts, appear on lawns particularly in areas of sandy
friable soil. This is the evidence that mining bees are at work and the most noticeable in parks and gardens is Andrenea fulva the tawny mining bee.
These bees have a life history which is very similar to that of mason bees. They are cavity nesting but use
pieces of leaf to line their nests and separate cells. They over winter as mature larvae and remain dormant until early summer when the adults emerge.
Solitary bees are beneficial insects and as such should be encouraged. There are ways in which artificial nests can be made and there are a number of attractive commercially produced nests which will enhance your garden. Planting flowers that bees like to visit will also attract them - such as early flowering heathers and flowering currant, lavender, sage, catmint, stonecrops, toadflax and fruit trees. It sometimes pays not to be too keen on weeding, as dandelions, daisies and dead nettles are also good sources of pollen and nectar.