Insects & other Arthropods David A Kendall   BSc PhD
E-Mail: kendalluk@aol.com
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Solitary Bees

Class: Insecta
Order: Hymenoptera
Most solitary bees resemble small honeybees or, in some cases, small bumblebees,
but the adults of most species are fairly short-lived and seen for only a few weeks
in spring or early summer . . . . . .

There are over 200 species of solitary bees found in Britain and, like the social bees (the bumblebees and the honeybee), they all feed on pollen and nectar and they are important pollinators of many garden flowers and commercial crops. Solitary bees have no 'workers' and each female builds only a small nest, which she stocks with a large quantity of pollen - enough to provide all the food needed by her future offspring. After laying her eggs, the female bee seals and abandons the nest and soon dies, leaving her offspring to develop on their own.

Many solitary bees nest in the ground and seal the nest with soil (these are commonly known as mining bees, e.g. species of Andrena). Others nest inside the hollow stems of plants or inside holes and crevices in brickwork, stone walls, dead trees, fence posts and other timber, sealing the nest with mud (mason bees, e.g. Osmia species) or pieces of freshly gathered leaves (leaf-cutter bees, e.g. species of Megachile). Leaf-cutter bees sometimes cause damage in the garden by cutting large, more or less circular holes in the leaves and petals of roses and other plants.

The Tawny Mining Bee (Andrena fulva) is one of several species, commonly seen around gardens in early spring, which dig nest burrows in lawns and similar places. This bee is about the same size as a honeybee, but covered with fairly dense golden hairs.

NEST HOLES NEST HOLE MINING BEE
Nest holes in a garden lawn (left & centre) excavated by the female solitary tawny mining bee, Andrena fulva (right)

The female bee makes a small volcano-like mound with the soil excavated from the nest. There may be many nests close together, giving the impression of communal life, but each female is actually working alone. Nesting activity lasts only a short time (perhaps 2-3 weeks), after which the small mounds of earth around each nest entrance soon disappear, with no permanent damage to the lawn. Take care not to confuse solitary bee nest mounds with the mounds of earth caused by the nesting activity of ant colonies. Solitary bee mounds have a single large entrance hole in the middle, and by watching for a short while on a warm sunny day, you will see the bees coming and going to collect pollen.

If left alone, these bees will often nest in the same area year after year, and provide an annual service by pollinating your early flowering fruit trees and shrubs (apples, pears, currants and gooseberries) and other garden plants - so helping to ensure good crops later in the year.

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Another group of solitary bees are the so called carpenter bees (Ceratina and Xylocopa species). These bees tunnel into plant stems and wood, often causing damage, and thus are less welcome around the home and garden. Most tend to be fairly gregarious with several females making their individual nest-tunnels close together. The lesser carpenter bees (Ceratina) are fairly small (5 mm or so in length), and usually black or metallic blue or green in colour. Most of them excavate nest-tunnels in the central pith of plant stems such as sumac and raspberry. The large carpenter bees (Xylocopa species) resemble large bumblebees in general appearance, mainly black in colour, but sometimes with dense yellow hair on the thorax (the body section where the wings attach - see below). These bees usually attack fairly solid wood (e.g. dead unrotted trees and tree-stumps, felled timber, fence posts, etc.). They sometimes tunnel into the timbers and beams of houses, barns and other buildings, and may cause considerable structural damage if left unchecked. Each bee excavates a large nest-tunnel, often over 30 cm long, divided off into a number of separate cells by partitions of chewed wood chips. Each cell is stocked with a mass of nectar and pollen on which the female lays an egg. Like other solitary bees, when nesting is finished the female bee leaves her eggs and grubs to develop on their own, through to the next generation of adults.

The great carpenter bee, Xylocopa virginica, is common in many parts of North America. This bee is over 25 mm long (about the size of a very large bumblebee), with dense yellow hairs on the thorax, a shiny black abdomen and brownish wings.

GREAT CARPENTER BEE

The blue carpenter bee, Xylocopa violacea, is found in southern and central Europe. It is also about 25 mm long, but glossy black all over with sparse black hairs. The opaque wings are dark brown with a lilac-coloured sheen.

BLUE CARPENTER BEE
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Copyright © 2010 David Kendall Last revised May 2010