Make a House for Solitary BeesPosted: May 30, 2011
What are Solitary Bees ?
As well as Bumblebees and Honeybees (that live collectively) there are some 200 species of wild bees in the UK that are called ‘solitary bees’ because they make individual nest cells for their larvae. Some species nest in small tunnels or holes in the ground or in sandy banks, piles of sand, or crumbling mortar. Others use the hollow stems of dead plants such as brambles, or tunnels previously bored into dead wood by beetles. Mason Bees and Leafcutter Bees are well-known examples and are common in gardens.
Solitary bees are harmless and do not sting, they do not live in hives or build combs, and they do not swarm.
If you find them (for example in old house walls) please leave them alone. Colonies are very faithful to their nest sites and may have been living there for many decades. They are part of the ‘fine grain’ of your local biodiversity – something to be cherished.
A number of species are commonly seen in gardens, and they are very useful as they pollinate fruit crops. It is easy for gardeners to encourage them. By drilling holes in dry logs or blocks of wood it is possible to create artificial nesting sites for them.
Constructing the House
All you need is a wooden box, open on one side, which is then fixed to a sunny fence or wall. You then fill it with blocks of wood or small logs in which you have drilled small holes. A variety of solitary bees will use these tunnels as nest sites. The box does not need to be deeper than 8ins, but must have an overhang at the top to keep rain off. You may already have a wooden box or a drawer from an old wooden chest of drawers that you can adapt for this purpose. If not, you can make one. The one in the picture is 8ins deep, 12 ins high at the front and 12ins wide, made out of untreated European spruce. I have given it a sloping, slightly overhanging roof to deflect rain.
I have not put a back on the example in photograph, because if you intend to fix the box against a wall or fence, you don’t need to put a back on it, or you can make a back of chicken wire, simply to help keep the wooden blocks in place. If the bee house is to be free standing, fixed to a pole, you will need to give it a wooden back, to give protection from rain and wind.
The dimensions do not have to be exact and you can make a larger bee house if you want. It is also possible to make a very large, free standing one, and pile up drilled logs and timber in it. (See photograph at foot of this page). For the structure of the house you can use any timber that you have to hand, so long as it has not been recently treated with a preservative. If you don’t have any timber around that you can re-cycle, builders merchants often have offcuts of wood available cheaply. Composite materials such as hardboard, chipboard or particleboard tend to disintegrate in the rain and are not suitable.
Inside the shell of the bee house you stack dry logs or sections of untreated timber, up to about 7ins in length, into which you have drilled a selection of holes of varying diameters between 2mm and 10mm, but no bigger. [Note that the diameter of the holes in some commercially sold wooden solitary bee houses is too large, and the bees cannot use them!] The open ends of these holes should face outwards, and must be smooth and free of splinters. If necessary use a countersinking drill bit to clean and smooth the entrance to each hole, as the bees will not enter holes with rough splintered wood around them. Carefully clean away any sawdust, as this will also put them off. If you are able to obtain extra- long drill bits and can drill deep holes into the wood you can make your bee house deeper, and stack longer sections of drilled logs and timber in it.
The bee house must be positioned in full sun, facing south east or south, at least a metre off the ground, and there must be no vegetation in front of it obscuring the entrances to the tunnels. The bees are cold- blooded and rely on the sun’s heat to warm them up in the morning, hence the need for a sunny site. They do not have furry coats to keep themselves warm like bumblebees do.
Bees Take up Residence
Different species of Mason Bees (Osmia) will occupy different diameters of tunnels. They will construct a series of ‘cells’ in each tunnel. In each cell they leave a block of pollen that they have collected from nearby flowers, lay an egg, and wall it up with mud they have collected from the ground nearby (see image of walled-up tubes below right). In dry weather make a small mud patch for them.
Later in the summer, Leafcutter Bees (Megachile) may also use the tunnels, lining their cells with circles of leaf that they cut from wild rose bushes. Include some holes of very small diameter (e.g. 2mm) and you will get various other small solitary bees using them. I suggest drilling some blocks just with very small diameter holes, or having a whole separate bee house of them.
You can also place commercial bee tubes in your bee house. These cardboard tubes are very popular with Mason Bees, but do not suit the smaller species. They are now marketed by a number of on-line suppliers, including CJ Wild Birds Ltd. (www.birdfood.co.uk) and Wiggly Wigglers (www.wigglywigglers.co.uk).
Bee activity will cease by mid-September at the latest. You can then remove the occupied logs and tubes and keep them in a cold dry place during the winter, to protect them from winter wet, replacing them in the bee house in March. An unheated shed, porch, or carport will do. This is very important – winter wet, not cold, is their enemy. Do not store in a warm place – they need to be cold and dry during the winter. Persistent wind-blown rain can dissolve the mud walls of the cells, and cause both wooden and cardboard bee tubes to rot. As autumns and winters are now very rainy, you need to ensure your bee tubes are protected from excessive wet. If your bee house has a good overhanging roof and is waterproof you can leave the tubes there. From April onwards, young bees that have over-wintered in a dormant state inside the tunnels will emerge, and start the cycle over again.
If you notice Woodpeckers or other birds attacking the tunnels looking for bee larvae, fix a piece of chicken wire across the front of the bee house. This does not seem to deter the bees.
Make a Bee Post
An even simpler alternative is to make a bee post – drill a variety of holes up to 12mm in diameter into the side of a thick piece of untreated timber, and fix to a sunny wall or fence. (See photograph). Again this should be kept in a dry, cool place in winter and brought out in March. If you like you can give it a roof to deflect rain. Smooth down the entrances to the holes thoroughly so there are no sharp splinters, as these will put the bees off. New fence posts from garden centres are unsuitable because they have been treated with chemicals, but lengths of very old fence posts or old roof joists, such as you often find on skips, are ideal. In my experience the bee post is not as popular with the solitary bees as as as the bee houses described above, but other people have good success with it.
Bundles of dead stems
Bundles of bamboo canes, sawn into lengths about 8ins long just below a joint may also be occupied by solitary bees, as will bundles of rigid dried stems of various herbaceous garden plants, especially raspberries, brambles, teasels, and elder. Some species of bees prefer these stems and will not use drilled holes. Rolls of dried reeds (sold as portable screens in garden centres) can also be cut up and placed in your bee house will be used by very small species of solitary bees. The bundles of stems must be kept completely dry at all times, under some sort of shelter – they will soon rot if exposed to rain. If you make a larger bee house you will have scope to include all of these nesting opportunities.
Buying Bee Houses
A number of commercially made wooden bee houses are available. Some of them are quite expensive, and one particular design does not work as the holes are too large! So beware wasting your money. The beauty of home- made bee houses is that you can use re-cycled or waste wood and logs and make them for virtually nothing. One commercially available model which is worth investing in if you are particularly interested has glass tubes for the bees to nest in. You can open a door and look at the larvae as they develop in their cells in the glass tubes. And of course the cardboard tubes that I mention above, and you can see in the illustrations above, are very popular with Mason Bees.
These are not for Bumblebees
Only solitary bees will use the kind of bee house I describe here. The needs of bumblebees are very different – their nests consist of communal wax combs, which they construct mostly in holes underground or in long tussocky grass. Bumblebee boxes are available from many wildlife gardening outlets, and some are hugely expensive – yet bumblebees rarely take to them. Beware wasting your money! Better to encourage the kind of flowery habitat, not over-manicured, that bumblebees like, and let them find their own nest sites. The website of the Bumblebee Conservation Trust has good advice about bumblebee nests, and how you can make inexpensive nest sites yourself. There is more information about Bumblebees on my BUMBLEBEES page.
A whole insect community
Various other sorts of parasitic solitary wasps and parasitic bees will find your bee house once it is occupied, preying on, or taking over, the nest cells of mason bees. Don’t worry about them, they are all part of the fascinating community of insects.
A larger Bee House
It is easy to make a larger house for solitary bees. I first saw one like this in Switzerland in the early 1980s. Since then I have seen them on several occasions in Germany and Switzerland, but curiously they are rare in the UK. It is time to put that deficiency right!
The one on the left is about 5ft (1.5m) high. made out of recycled wood with part of a disused fence panel at the back.
For more info about some common solitary bees and what flowers will attract them, please download the ‘World of Wild Bees’ fact sheet from my fact sheets page.
There is also an excellent website about the different kinds of solitary bees you are likely to see in your garden at www.insectpix.net
It’s mainly in the details of choosing plants that are suitable for your region and appropriate for your local wildlife that you need to seek local advice. Many of the plants recommended for wildlife gardens in Britain are not suitable for North America.
For example, several well-behaved British wild flowers that are often recommended in the UK as bee and butterfly plants are highly invasive in North America and planting them is banned.
On the other hand, there are many scarlet, trumpet- shaped flowers such as Penstemons, Monardas, Pentas, Epilobium canum, Lonicera sempervirens and Lobelia cardinalis, that are of little or no use to wildlife here in Europe, but are perfect for many North American gardens as they will attract hummingbirds.
Pentas is illustrated on the masthead above, being visited by a female Costa’s Hummingbird. We don’t have hummingbirds in Europe – you are so lucky to have these fascinating litle birds visiting your gardens.
I reproduced this item with permission from “The Pollinator Garden”, www.foxleas.com
© Marc Carlton 2011.