As well as Bumblebees and Honeybees (that live socially) 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 of solitary bees that are common in gardens.
Some species of solitary bee species will group their nest cells together in aggregations, and a few have evolved social behaviour rather like bumblebees. Many solitary bees are very small and you may not have realised they are bees. All collect nectar and pollen from flowers, except the so-called 'cuckoo' species that lay their eggs in the nest cells of other species.
Solitary bees are harmless and not aggressive. They rarely if ever sting unless trodden on or squashed between your fingers and they do not have painful stings like those of honeybees. They do not live in hives or build honeycombs, 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 a number of common species, particularly Mason Bees.
These bee houses are also called 'trap nests', or in America, 'bee condos'. It has become fashionable to call them 'bee hotels' but I feel that this is misleading, as they are not short-term accommodation like a hotel room, they are the bee's permanent home for nine months or more of its short life as it develops from an egg through a larval stage, into adulthood.
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. It is really important to protect your bee nest tubes from heavy persistent rain.
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 off cuts 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. This is very important. If necessary use a countersinking drill bit, or sandpaper, 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. Again this is very important. Solitary 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.
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. Their habit of using mud as a plaster to wall up their cells led them many years ago to be named Mason Bees, 'mason' being an old word for a builder of plasterer.
Their name has nothing to do with 'masonry', in fact they do not live in brick walls as a rule. If you have solitary bees living in old mortar in a wall they are more likely to be Anthophora plumipes or Anthidium manicatum,. Download the wild bee fact sheet from my fact sheets page for more about these two species.
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.
In the picture above a Leafcutter Bee has walled up the cell at the top and a Mason Bee has walled up the cell below with mud.
When you drill holes in logs or posts, make sure you include plenty of holes of smaller diameters (down to 2mm). If you like you can drill these in separate pieces of wood or have a completely separate bee house for them. You will get various other species small solitary bees using them. The smallest holes will attract the Harebell Bee (Chelostema campanularum) during June and July. In the wild this species uses holes in dead wood vacated by the Furniture Beetle ('woodworm'). Using the smallest drill bit I could get I drilled the hole shown in the image on the right. It is being examined by a Harebell Bee (much enlarged).
You can also place commercial bee tubes in your bee house, as illustrated on the right. These cardboard tubes are very popular with Red Mason Bees, but do not suit the smaller species. They are now marketed by a few on-line suppliers, such as CJ Wild Birds Ltd. (www.birdfood.co.uk).
Bee activity will cease by mid-September at the latest; Mason Bees earlier. Inside the tubes and tunnels, each cell will have been provisioned with a mixture of pollen and nectar by the mother bee and a tiny egg has been laid. The egg soon hatches and the larva develops rapidly by eating the the nutritious mixture of pollen and nectar. The larvae then pupate. Osmias will spend the next 9 months or so in a dormant state as pupae, until they are ready to emerge as adult bees the following spring or summer. Some other species such as Anthophora spend most of this period as fully-formed but dormant adults.
You can 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 blocks and cardboard bee tubes to rot, and the young bees will succumb to fungus diseases. As autumns and winters can be very rainy, you must ensure your bee tubes are protected from excessive wet. If your bee house has a good overhanging roof and is rainproof you can leave the tubes there. Otherwise they must be moved somewhere cold and dry during the autumn and winter. From April onwards, young bees that have over-wintered in a dormant state inside the tunnels will emerge, and start the cycle over again.
Many of the elaborate 'insect habitat hotels' now shown in gardening programmes on TV, in magazines and at gardening shows such as Chelsea are ornamental rather than functional I'm afraid. Unless they incorporate serious shelter from winter wet including a robust roof, the wood will become saturated and the structure will not be suitable for over wintering insects such as solitary bees.
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.
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 left outside to endure winter rains these small posts can soon get too damp. 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 the bee houses described above, but other people have good success with it.
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.
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. And of course the cardboard tubes that I mention above, and that you can see in the illustrations above, are very popular with Mason Bees.
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.
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.
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. I made it out of recycled wood with part of a disused fence panel at the back. It has an overhanging tile roof to deflect rain.
On the continent wildlife gardeners also build special bee walls of soft mortar for species that tunnel in mortar or cliffs and don't like logs. Again, time to introduce such walls to the UK.
For more info about some common solitary bees and what flowers will attract them, download the 'World of Wild Bees' fact sheet from my fact sheets page.
For links to sites with images of wild bee houses around the world and lots of other cool stuff to do with wild bees, take a look at this site: Resonating Bodies.
Even more information and fact sheets about bee homes and the conservation of various species wild bees in the UK are available from Hymettus Ltd, a conservation charity for wild bees and related insects.
If you are reading this page in the USA or Canada, you have different species of solitary bees to those here in the UK, but lots of them will benefit from providing nest sites exactly like the ones I describe here. On my North America page there are some more links to sites that will tell you about solitary bees and other pollinators in your countries.
© Marc Carlton 2011. You may print this page for personal use or for non-commercial, not-for-profit educational purposes. Other reproduction is prohibited without permission.Contact