Bumblebee nest boxes and nest sites
Most natural bumblebee nests are down a small tunnel in part or all of an old mouse or vole nest, or they will be in the dry base of a grass tussock or untidy hedge bottom. Gardeners ruin these desirable residences by being tidy.

Providing nest sites - Making a nest box - Food - Siting your nest box - Success and failure

Providing nest sites

Bumblebees like to nest in warm, sheltered sites, different species have differing nest preferences, however the easiest ones to provide for are the ground and surface nesters.

The bumblebee on the the right is a Bombus terrestris, though you wouldn't know it from the photograph as she is so covered in pollen. B. terrestris tend to have large nests that last for a few months. They are also the species that are sold commercially to pollinate crops, as they are considered the easiest species to domesticate. Every tomato you eat has been pollinated by a bumblebee. Usually terrestris nest at the end of a tunnel leading to an abandoned mouse or vole nest.

• Don't be too tidy, that small pile of twigs and leaves may look like rubbish to you, but it might provide a home to a colony.
• An upturned flowerpot with a roof slate and some nesting material could provide a nest site. The very best nesting material is the contents of a mouse or other small mammal's nest, but clipped pieces of dried grass or dry moss will do. It is important that there are no ant nests close by as they will rob the bumblebee nest in the early days.
• An old teapot buried in the ground with the spout providing an entry tunnel makes a good secure nest site if it can be kept free from damp.
• I have heard from some people in the US that their bumblebees prefer to nest in north facing sites. This is probably due to the hotter summers they are lucky to have, or some UK residents might say it is simply due to the fact that they have summers! Whereas in this damp, green island summer sometimes happens one warm sunny afternoon and is gone till next year.

Box size

For a single chambered box the minimum size is 15 x 15 x 15 cm, the largest size is 25 x 25 x 25 cm.

Space between the box and the nest

Ventilation is very important. The brood will be kept at a temperature of above 30^oC regardless of the temperature outside, so there is a need to get rid of the condensation. Apart from the entrance/exit hole there will need to be at least two ventilation holes. These holes must be covered to prevent the entrance of ants which could destroy a nest in the early days. So cover the holes with some form of netting. Nylon net curtain material fixed with glue is one of the simplest methods. Do not use cotton as ants can cut through this, also it rots with time.

Chicken wire is a good way of forming a cage for the nesting material, and of keeping the nesting material off the ground and away from the sides of the box. A layer of small pebbles at the base of the nest helps drainage, and if the nest is to be buried a drainage hole under this is also a good idea. Again all holes except the entrance/exit must be netted against ants.

Even though you have all of these holes you must still prevent the rain from entering, and one of the simplest ways of doing this is to use a roof slate or something similar.

Entrance/exit size is not too important as long as it is big enough for a large bee to crawl through. If you are placing the nest underground or if you want to attract the bees that like a tunnel then make the entrance hole as big as the tubing you use for the tunnel. The clear plastic tubing found in DIY shops is ideal to use for this. It is quite easy to fool bumblebees into thinking the nest is buried by potting sods over the tubing.

Another thing you can try is to scrape away the grass or soil just at the entrance of the tubing. Your aim here is to make the entrance look like it has been used by a mouse or vole. You can even scatter mouse/vole droppings if you wish. Bumblebees nest in the dark, so if you want to build a box with a Perspex top for observation do also make a cover for this to keep out most of the light.

The nest

The nest must be kept dry. The optimum temperature for

larva is 32^oC, so unless the nest box is indoors the queen needs nesting material that will provide enough insulation. She will modify and arrange what is there, but she will not add to it. So the amount and kind of nesting material is crucial.

Do not use synthetic fibres as these will just entangle the bees and kill them. Suitable nesting materials are dried moss, upholsterers wadding, horsehair stuffing out of old chairs, kapok, bedding for small rodents, old mouse/vole nest. You can use just one or a combination of these. For extra insulation a fluffed-up layer of coarser material can be placed on the bottom of the box to create a dry layer. On top of this place a ball of fluffed up nest material. The size of the ball should not be so big that is touches the side of the box. Push your thumb a little way into the ball and place this depression towards the entrance so that the queen find this as she enters. Don't be too fussy though as she will rearrange things to suit herself.

Bombus pratorum, see the male above, have a small nest, and do not require a tunnel. In fact pratorum are noted for nesting in unusual places, rolled up carpets, bird nest boxes, underneath lawn mowers that have not been cleaned. So pratorum would probably be happy with nest material no bigger then a tennis ball. Bombus terrestris, right, would require a tunnel and a larger amount of nesting material.

Food

You do not have to provide food, but if you want to give the queen a helping hand at the start of the nest you can. Make a mixture of around 30% honey and 70% water and place it is a small container. The plastic top of a lemonade bottle is fine. Glue a piece of netting over this to prevent the queen falling in or getting wet. The plastic netting used for onions is ideal. You must change this food every second day, so it must be placed where you can easily get to it. Also the nesting material must not fall into it or come into contact with it. The best way to do this is to have a double chambered nest box. One, larger chamber for the nest and a second, smaller empty chamber for the food. The bees may also use this second chamber as a latrine. If you place a piece of cardboard on the base you can easily clean it out.

Siting your nest box

The next box must be in position by early spring, even though some queens will not emerge from hibernation until later. Avoid placing it in direct sun, and try to keep it sheltered from the wind. A hedge bottom, raised bank, under a garden shed are all good places. Different species tend to have different preferences for nest location. These

preferences can be roughly divided up into 3 types - underground nesters, ground nesters and above ground nesters. So if you already know which species of bumblebee you have coming to your garden, or which species you would like to encourage, you can place the nest in a suitable spot.

Above ground nesters include Bombus pratorum and B. hortorum, ground nesters tend to be the ginger species, i.e. B. pascuorum, and below ground nesters are B. terrestris and B. lucorum. However I have found a B. lucorum nest half way up an old wall, and B. pratorum is notorious for nesting just about anywhere.

In the early days of the nest it is estimated that a Bombus terrestris queen may have to visit as many as 6000 flowers per day in order to get enough nectar to maintain the heat needed to brood her eggs. And during every foraging trip the brood will cool down, so the trips should be short. This is why it is vital that the nest is located close to rewarding flowers.

Success and failure

I have to be honest here. The success rate of artificial bumblebee nest boxes is low. A Canadian study had only 7% of their nest boxes occupied, however another group had 30%. This web site has been running for ten years, and it is only now that I have made this page as so many garden centres are selling bumblebee nest boxes. If you have bought or made a box and have followed the advice above and still have had no success, then don't give up. Leave your box out all winter. A mouse may nest in it. If in the spring you find no trace of occupancy of any kind then it is probably not well sited. If you do find trace of a mouse or vole then this is a good sign. Keep any bits of bedding, and add a little more if you think it is needed.

If your nest was successful last year it can still be used again. There is very little you need to do. Just check it out and remove any bits of debris and any dead bees that the scavengers haven't cleared away. Add more nest material if necessary, and that's it.