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Encouraging Solitary Bees

Published in Organic Gardening Magazine - April 2005

In these days of increasing awareness of the benefits of organic gardening and farming, biological control is big business.  Introducing beneficial insects into our gardens or greenhouses is now a fairly normal approach to pest control or pollination, and in certain situations can be a very effective way of dealing with unwanted insects such as whitefly or aiding the setting of tomatoes. But however useful this scientific approach may be, many gardeners would still prefer to encourage useful creatures using natural methods, building up a well balanced garden over time, rather than introduce predators in unnatural quantities or bumblebees into areas where natural pollinators are lacking.  If we can encourage these insects to colonise our gardens naturally there is more likelihood that the environment will be right for them and their populations will increase. As far as pollinators are concerned there are over 260 different species of bee in this country, but at least a quarter of these are in serious decline, mainly due to lack of wildflowers in meadowland and hedgerows on which they forage for pollen and nectar. Bumblebees, solitary bees and honey bees all need a good supply of these plant foods, for themselves and their larvae, and the all important pollination occurs as they move from flower to flower.  It therefore stands to reason that a good supply of nectar and pollen producing plants is a first step towards establishing plenty of pollinators of all types.

honey bee

Most of us know something about honeybees and bumblebees but pollinating solitary bees are a particularly useful group of insects and it is not difficult to cater for their needs in any garden.  Many species occur in small numbers in gardens and on allotments, and populations of these useful insects can be encouraged to increase by providing the food and conditions they require.  One of the solitary bees, the red mason bee, Osmia rufa, has been much in the limelight recently on account of its ability to work garden plants, especially fruit trees, and pollinate more effectively than either honeybees or bumblebees.  It has been estimated that a single red mason can do the work of over 100 honey bees, working more quickly and flying at lower temperatures, making a small colony of these insects a great asset to fruit growers.  However, the red mason bee is only one of the species of solitary bee that naturally occur in gardens.  Another species, the blue mason bee, Osmia caerulescens, is an effective pollinator of flowers, herbs and vegetables and along with the red mason is also found in gardens in small numbers.  There are many other species and each has its own place in the garden or allotment habitat.  Encouraging a wide range of these bees means that pollination throughout the growing season can be effectively covered.

Many of the solitary bees will nest in artificial homes.  Red and blue mason and leaf cutter bees in particular are easy to cater for, and nest homes can be made for them quite easily by using a few things readily found in the home or garden, ranging from off-cuts of softwood and hollow plant stems to empty baked bean tins.  To make a simple bee nest home, completely remove the lid of a tin can and wash the tin thoroughly.  After drying, paint the inside end with a waterproof adhesive and pack the tin tightly with large diameter paper (not plastic) straws, each one about a centimetre shorter than the tin.  The completed home should be painted on the outside to prevent rusting, and then attached with string or tape to a south facing, bee friendly spot such as under the eaves of a wooden garden shed.  It is usually recommended that these homes are sited at about chest height, but I have effectively used them beneath a sunny downstairs windowsill.   A south facing woodpile in the garden is also the sort of place that female bees may be house hunting.  

red mason bee

This type of home can be packed with sections of hollow bamboo cane or plant stems as an alternative to straws.  I prefer plant stems from species such as hogweed or sweet cicely, which are cut to size in the late winter and left to dry in a sunny shed or greenhouse.  The natural variation in the diameter of the stems will encourage a range of bees, rather than one species.  If you prefer a completely natural looking home, a triangular box made with wood off-cuts and a plywood back works very effectively.

An alternative home can be made by drilling a series of holes in a 5cm square piece of softwood, about 15cm in length.  Use the longest drill bits you can find, and make holes between 7 and 10mm in diameter.  This can be placed in a pile of logs or attached to a fence or shed, again south facing.  If you would rather buy a superior bee home, there are now plenty available from garden centres and mail order catalogues specifically for red mason and other solitary bees.  As the red mason is a slightly larger insect she requires tubes of a larger diameter.  The female red mason bee, recognisable from the fuzz of gingery-red hairs on her body, will be seeking a nest site in March and April.  After mating, each solitary female will lay single eggs inside the tubular holes, sealing each one into its chamber with a quantity of pollen for the larvae to feed on.  The ends of the chambers are sealed with mud, which she carries to the nest in her jaws.  The blue mason bee seals her nest chambers with a glue made of chewed leaves.  Later in the year the leaf cutters (species of Megachile) will use vacant holes in the same nest home, filling the ends with circular sections of leaves carefully cut from roses, willow herb and other common species. 

leafcutter bee

The life cycle of these useful insects is fascinating and complex.  The young bees remain inside their chambers until the following spring when they hatch and begin the job of pollinating your garden fruit, flowers and vegetables with great efficiency.  Actively encouraging them to your garden or allotment and building up a population by providing them with breeding homes and food will ensure that your fruit and vegetables set in the natural way that nature intended.

Grow a selection of bee plants to encourage as many species of bee as possible to your garden.  Here are some of the best:

Herbs especially rosemary, lavender, borage, hyssop, mint, thyme and marjoram

Annuals and biennials including wallflowers, poached egg plant, mignonette, and phacelia

Perennials especially cranesbills, dead nettles, fleabane and globe thistle

Wildflowers especially knapweed, vipers bugloss, clover, scabious, vetches and trefoils