Red Mason Bees, Osmia rufa: Ethical Management of
Pollination in the Veganic Garden

Chris O'Toole

(Head of the Bee Systematics and Biology Unit, Oxford University Museum of Natural
History and Chairman of the Oxford Bee Company)

It is now possible to provide nests for the Red Mason Bee, Osmia rufa and in so doing, be proactive in the ethical management of pollination in your garden. And at the same time, you will be helping to conserve not only this very efficient pollinator of fruit trees and spring flowers, but also several other wild bee species which will also use these nests.

Background

You may have read Pauline Lloyd's article in The Vegan News (May 1999) about honeybees and those aspects of their management which may be issues of concern for the veganic gardener. Pauline also wrote of the current plight of some of our formerly common bumblebee species which are now undergoing a serious decline and how this is almost certainly due to modern intensive agricultural practice.

It is not only the bumblebees which are under pressure: of the 267 species of wild bee native to Britain, 25% are listed in the Red Data Book¹ as endangered.

The time is ripe, therefore, to draw attention to measures which the veganic gardener can take to help conserve bees, on whose life-sustaining relationships with flowering plants we all rely: every third mouthful of human food is dependent on the unmanaged pollination services of bees².

What you can do

The simplest thing you can do to enhance wild bees in the garden is to grow plants which they particularly like and Pauline mentioned some of these when discussing the plight of our bumblebees. It is now possible to take more steps in this direction by supplying nests which will provide homes for several of our wild, native bees.

The bees which are attracted to these nests are two or three species of mason bees (Osmia spp.) and two or three species of leafcutter bees (Megachile spp.). However, the commonest and most frequent nester is the Red Mason Bee, Osmia rufa, which is an efficient pollinator of fruit trees, many garden flowers and vegetables, especially onions grown for seed.

How do the nests work^3,4

The nest kits mimic the natural nest sites of these bees, which are pre-existing cavities such as hollow plant stems and beetle borings in dead wood. They will also nest in irregular erosion holes in stones and flints and old nail holes in the mortar of soft walls. Osmia rufa often nests in old walls, but does not actively excavate into old mortar. It simply uses existing cavities, but in so doing, sometimes takes the blame for a mining bee, Colletes daviesanus, which does actively dig and, in large numbers, can cause some damage.

Nest kits are supplied by the Oxford Bee Company (see below) and come in two sizes: 30 and 100 nest tubes. Each nest tube comprises an outer cardboard tube and an inner white paper liner, with a black plastic cap at the rear end. The tubes are packed into a plastic cylinder which it closed at one end.

The cardboard tubes and paper liners are made from re-cycled pulp and the plastic holding canisters are made of PP plastic, in anticipation of forthcoming EU legislation on the use of environmentally- friendly plastics.

Life history

Osmia rufa is a solitary bee. That is, each nest is the work of a single female, working alone. There is no caste of workers. Nevertheless, the species is gregarious. That is, females seem to be attracted to sites already being used by other females.

The species has an annual life-cycle and is active in spring and early summer, from late March to the end of June. It is widespread in England and Wales and occurs as far north as Edinburgh. It is absent from Ireland, but extends across the whole of Europe and even penetrates south into the Mediterranean Basin.

Both sexes are densely clothed with reddish brown hairs, with the male having a dense tuft of white hairs on the front of the head and the female's head being entirely black haired. Males are 6-11mm long, while the more robust females are 10-16mm in length.

A female Red Mason Bee,Osmia rufa,
gathering mud for nest building purposes

Males emerge a few days before the females and patrol flowers and
nest sites in search of newly-emerged virgin females. After she has mated, a female searches for a nest site. Having found a suitable nest cavity - either a hollow plant stem, beetle boring in dead wood or an Oxford Bee Company nest - the female finds a suitable patch of bare soil as a source of mud, which she uses to plug the rear of her nest tube.

She then gathers pollen at flowers and transports it back to her nest compacted in the scopa, a specialised tract of hairs on the underside of the abdomen. About 10 to 12 foraging trips are sufficient to provision this first cell. She then lays a single egg on the pollen mass and seals the cell with mud. She repeats the process until she has built and provisioned a linear sequence of 8-10 cells, each partitioned from its neighbour by a wall of mud. Finally, she seals the completed nest with a plug of mud. A female might make 4-5 nests in her lifetime.

Being a typical solitary bee, she will not live to see her offspring. She will die towards the end of June. By this time, the eggs will have hatched out and the larvae will be eating the stored pollen. Each larva moults its skin four or five times as it grows in size.

By the end of August, the full-grown larva is ready to pupate and, immediately before doing so, spins a tough, brown silk cocoon. The process of pupation involves the breakdown of larval tissues and their reforming into the final, adult structure.

The pupa becomes an adult bee at the beginning of October and remains within the cocoon until the following spring, when it emerges to begin the cycle anew. A high proportion of the females of this new generation will remain loyal to their natal nest site and will re-use the nest tubes of their maternal generation.

Why is Osmia rufa such a good pollinator?

The Red Mason Bee is an excellent pollinator of rosaceous fruit crops and a wide range of garden flowers. So far as fruit trees are concerned, it has a number of advantages over the honeybee as a managed pollinator:

A female Red Mason Bee, Osmia rufa,
gathering nectar from a flower of borage,
Borago officinale.

• It flies at temperatures below which the honeybee is grounded.

• At any given temperature, it visits more flowers per minute than the honeybee.

• On any given foraging trip, a female Osmia rufa is more promiscuous in terms of the number of trees visited than the worker honeybee.

• Osmia rufa does not store honey in its nests: it is entirely pollen driven and uses nectar only as an energy source to satisfy immediate needs, so, unlike the honeybee, it always scrabbles around for pollen when it visits fruit blossoms.

• Osmia rufa is not as efficient as the honeybee in grooming itself, so when visiting flowers, is much more heavily dusted with pollen and so the chances of pollination are greater.

• Because its pollen collecting apparatus is situated on the underside of the abdomen rather than on the hind leg, there is a greater chance of pollen coming into direct contact with receptive stigmas of flowers.

• The peak of activity of Osmia rufa coincides with the flowering of all the major orchard fruits.

Why should the Red Mason Bee appeal to the veganic gardener?

In providing nests for this bee, one is not interfering with or modifying its natural behaviour: one is simply saving it the time and energy that would normally be spent in searching for randomly and sparsely distributed natural nest sites.

At the same time, one is aiding the conservation of wild bees and enhancing the pollination status of the garden. And because this bee does not store large amounts of honey, it does not have huge resources to defend and is therefore very docile. It is quite safe with children and pets.

Where can I get nest kits for the Red Mason Bee?

Some Good Websites:

• Buckingham Nurseries
  
• The Vegan News (May 1999) - Article: All about bees and their products.

Further Reading:

• ¹ Falk, S. 1991. A review of the scarce and threatened bees, wasps and ants of Great Britain. Research and Survey in Nature Conservation 35 : 1-344. Nature Conservancy Council, Peterborough.

• ² The Forgotten Pollinators, by Stephen L. Buchmann and Gary Paul Nabhan, Shearwater Books, 320pp., 1997. £16.99. [An excellent account of just how we depend for 80% of our food on the unmanaged pollination services of wild bees and other insects and just how much the life-sustaining relationships between bees and plants is threatened by human degradation of habitats.]

• ³ The Red Mason Bee: Taking the Sting out of Beekeeping, by Christopher O'Toole, Osmia Publications, Banbury, 34pp. £3.95. [A practical guide to the managing Osmia rufa as a pollinator in gardens, allotments and orchards. Obtainable from the Oxford Bee Company]

• ⁴ Bees of the World, by Christopher O'Toole and Anthony Raw, Blandford Books (Cassell), London, 192pp.,1994, £15.99. [A comprehensive and highly illustrated account for the layman of the fascinating natural histories of bees from around the world.]

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