Bumblebee nest boxes and nest sites

Providing bumblebee 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. To find out the nesting preferences of individual species go to the species page and use the photographs to discover more about the species you have in your garden.

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. Many gardeners ruin these desirable residences by being too tidy.

bumblebee nest in loft insulation

Making a bumblebee nest box

Artificial nest boxes consist of two main parts, the box and the nest. Natural nests do not have a "box", the box is the surrounding soil, the grass tussock, etc. The material you use is unimportant. Wood is the favourite, but plastic, or metal are also possible. Two plastic flowerpots joined together make an inexpensive nest box, as do large metal cans with some form of lid. And the easiest option is an old bird box - the kind used by blue tits has a good entrance size - then put in a wad of upholsterers cotton or chopped up dried moss. I have made some drawings of how to make inexpensive nests on the nestbox plan page. The nest on the left is in loft insulation.

Detailed plans of nest boxes can be found in the books by Sladen and Intenthron; there is also some information in Prys-Jones, and Kearns. Full titles and publishers can be found on the book page, or visit the sites below.

  • http://www.hymenoptera.de/nuke/html/index.php
    ?newlang=eng
    This is an excellent German site, but with a large amount translated into English. You can find good plans for bumblebee boxes, advice on recognising nest-searching queens, and much more. The site is really not just about bumblebees, but all the Hymenoptera, and well worth a visit.
  • Coffee can cottages. How to make a nest for bumblebees and other insects.

Bumblebee 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 30oC 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 putting sods over the tubing. Garden hosepipe is also good.

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. Bumblebees cannot see into the red wavelength of light, so if you want to observe without disturbing them cover the observation plastic with red film, or if the box is in a darkened she you can use a head torch with a red light.

The bumblebee nest

The nest must be kept dry. The optimum temperature for larva is 32oC, 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 (carder bees are the exception). So the amount and kind of nesting material is crucial. You do not need to provide a heat source, though. The queen, and later her daughters will brood the eggs and raise their temperature. For more about how young queens just starting a nest can keep the eggs at such a high temperature while outside it frequently drops below zero see the lifecycle page.

Do not use synthetic fibres or cotton wool 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 nests, bird nests in bird boxes.

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 it 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 finds this as she enters. Don't be too fussy though as she will rearrange things to suit herself.

Bombus pratorum, has a small nest, and does 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, I've even found one in a fuse box. So pratorum would probably be happy with nest material no bigger then a tennis ball. Bombus terrestris, would require a tunnel and a larger amount of nesting material.

Bumblebee 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 in 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 corrugated cardboard on the base you can easily clean it out.

Siting your bumblebee 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.

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.

Bumblebee nestbox predators and symbionts

If you are unlucky enough to have a bumblebee nest invaded by the wax moth (see the photograph on the right, the very best thing you can do for bumblebees the following year is to prevent any wax moth caterpillars hatching out as adult moths and breeding.

So destroy the entire contents of the nest box. Clean out the box. Then replace it as it was obviously well sited. Then leave the cold and winter to get at it.

Little reddish mites are not usually predators. They are scavengers, and so can be left alone.

For more bumblebee predators see the predators page.

 

Bumblebee nest destroyed by wax moth caterpillars

Tips for making your garden an attractive nesting site

  • 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 - see nestbox plans. 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. So in colder climates a south facing site is better.

Success and failure with bumblebee boxes

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%. And closer to home, at Stirling University Gillian Lye had just 3.1% of her nest boxes showing any kind of occupancy, never mind going on to produce new queens for the following year.

This web site has been running for ten years, and it is only now (2006) that I have made this page as so many garden centres are selling bumblebee nest boxes, and I get so many emails asking for advice about them.

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 traces 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.