Insect Identification sample sheet

The spaces beneath roofing tiles and behind ventilator grills in walls are also occasionally used as nesting sites by the Red Mason Bee. Females use naturally-occurring holes in either the bricks themselves or, more usually, in the mortar joints (especially soft mortar, with a high lime or sand content). Some females may also be able to excavate burrows in intact but soft mortar. Nesting burrows are excavated or enlarged by use of the bee's mandibles, and the resulting spoil is kicked out of the burrow entrance. These bees do not eat the mortar or brickwork, as has sometimes been reported! Some of these bees also construct their nests in holes in paths, the sides of sand pits or in coastal cliffs. Others are opportunists, utilizing almost any cavity of a suitable size, for example nail holes, beetle emergence burrows in timber and even the insides of locks. None of these bees is confined entirely to masonry.

Life-cycle

Nests in mortar generally consist of a single burrow, or a series of branching burrows each terminating in one or more circular or oval chambers known as cells. Where more space is available a honeycomb-like aggregation of cells may be built by the Red Mason Bee. A completed nest usually contains about six to twelve cells, the number varying with the species and the site chosen. The cells are provisioned with a mixture of pollen and nectar, and an egg laid on this 'pollen loaf'. When completed and provisioned each cell is sealed, usually with soil. Depending on the species, the winter is passed either as newly developed adults which remain for this period in their unopened cells (as in most spring-flying bees), or as full-fed larvae (summer-flying bees).

Damage and control

Although these bees are solitary nesters (ie each female establishes and provisions her own nest independently of others), they sometimes occur in aggregations, with nests very close to one another. The activity around very dense aggregations of Colletes daviesanus may resemble a small swarm of honeybees. The annual burrowing activities of numerous bees undermines brickwork and in rare instances (mainly Colletes daviesanus) can seriously weaken the fabric of a wall, perhaps eventually leading to its collapse. In practice this rarely happens as remedial action usually intervenes. The sight of bees milling about a wall is the most obvious sign of the presence of these insects, but excavated mortar (which collects in heaps at the base of the brickwork) presents a further clue to their presence. The most effective means of eradicating the problem is to rake out the affected mortar to a depth of about half an inch and repoint with a hard cement into which they cannot burrow. However, an easier method may be to harden the existing mortar by application of sealing fluid which can be painted onto the joints. Insecticides may not be effective.

Apart from the damage that these insects may cause to buildings, all mason bees are harmless to humans. Females have stings but are not aggressive and will never attack; to be stung you would have to squeeze a bee between your fingers!

Brief summary of some common mason bees

In Britain nearly twenty species of solitary bees have been found nesting in masonry. Of these, six species are usually the most frequently encountered, their headquarters being in southern Britain. These are:

The Wool-carder Bee, Anthidium manicatum

Large, robust species, body length 9-12 mm. The head thorax, abdomen and legs are black but extensively marked with yellow. The white pollen-collecting hairs of the female are restricted to the ventral surface of the abdomen, where they form a broad brush. Nesting females strip the long, woolly hairs from the leaves and stems of plants such as Lamb's Ear, House Leek, Yarrow and Aaron's Rod. The bee uses her toothed mandibles to shear off the hairs, these being carried back to the nest site as a small ball. In walls, the nest site is an existing cavity. Within this the hairs are teased out by the mandibles and the abdomen tamps down this fibrous layer to form the cell walls. 'Carding' is a term used in the textile industry to describe the teasing out of woollen or cotton fibres with a comb-like tool. This species flies from late May to the end of August or early September. It is locally common in England and Wales, rare in southern Scotland; absent elsewhere in the British Isles.

The Hairy-footed Flower-bee, Anthophora plumipes

Large, long-tongued species resembling a small bumblebee; body length 14-17 mm. Female has body hair entirely black, outer surface of hind leg with golden hairs; body hair of male mainly a rich brown (face bright yellow). Common in gardens where it mainly visits deep-throated flowers. Cell walls consist of a conglomeration of fine particles of soil or mortar which are probably bound together by a secretion from an abdominal gland. This bee flies, with a shrill hum, from mid March to the end of May, rarely June. It is distributed throughout much of England and Wales (especially in the south); absent Scotland and Ireland.

Colletes daviesanus

Medium-sized, short-tongued 'mining' bee; body length 8-10 mm. Dorsum of thorax with dense, reddish-brown hairs; abdomen appearing largely hairless, but dorsal surface of each segment fringed posteriorly with a narrow, white, hair-band. The cells of this bee are lined with a secretion from an abdominal gland; this liquid rapidly dries, forming a thin, waterproof and transparent membrane which is similar in appearance to cellophane. The species flies from mid June to mid September. Occurs commonly in England and Wales; local in both Scotland and Ireland.

Lasioglossum smeathmanellum

Very small 'mining' bee, almost hairless and mainly a metallic green; body length 6-7 mm. In masonry, the cell walls are probably formed from compacted mortar particles. The species flies from March or April to early September. Common in southern Britain, rarer in the north; absent Scotland and Ireland.

Megachile centuncularis

Medium-sized 'leafcutter bee'; body length 9-12 mm. Both sexes with a sparsely-haired black body integument; underside of female abdomen with a dense, brush-like clothing of long, red hairs. Cell walls fashioned from layers of neatly cut, green leaf sections (commonly rose in urban gardens). This bee flies from May or June to the end of August. Found throughout most of England and Wales; uncommon in Scotland and Ireland.

The Red Mason Bee, Osmia rufa

Length 7-14 mm. Both sexes clothed with dense, reddish-brown hairs. Pollen-collecting hairs of female confined to venter of abdomen. Face of female bears a pair of conspicuous, anteriorly-directed, prong-like processes. The cell walls are built from mud, carried to the nest site as small pellets held in the mandibles. The species flies from April to May or June. A very common bee in southern Britain, sporadic in southern Scotland; absent from central and northern Scotland and the whole of Ireland.

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This information has been produced by the Insect Information Service of the Natural History Museum. For details of our advisory and identification services, please contact:

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