You can also recognize queens who look for a nesting place by their behavior. They will fly from hole to hole (in the ground or in walls) looking for a suitable place for a nest.
Having a nest of bumblebees in your garden is not a bad thing. They are very docile creatures that will ony sting you (yes they can sting!) as a very last form of defence when you attack them yourself. Most of the time, they will try to fly away from you or they will drop on their back on the ground with their stinger pointing at you.
If you are an avid gardener, then you should welcome these animals with open arms. They are one of the best pollinators in the animal kingdom. They actually outperform bees. Firstly because they have longer tongues, so that can get in deeper flowers and secondly because of their ability to carry more pollen. They also can't tell their kin where the best flowers are. So bumblebees will go from flower to flower much more than bees, who home in on the best spots.
Having a nest box near your vegetable patch could increase your crops in a significant way. These boxes can hold between 50 and 600 bumblebees (depending on their species) and they will pollinate your garden for about 8 to 10 weeks.
You can buy commercially bred bumblebees in a box for pollination, but in this Instructable I'll tell you how to build your own box and how to start your first bumblebee population.
Step 1: Building the box
Bumblebees are not very fussy when they choose a nest, but they like a place with a long entrance (some of them can dig tunnels of more than 2 meters to their nest) or a vestibule.
The measurements of the box are not an exact science. My boxes are 350mm long, 196mm wide and 170mm high, but you can alter these dimensions to match bits of leftover wood you have lying around. The only things that are important are, that the entry hole should be about 25mm in diameter and that the nest chamber itself should not be smaller than 150mm x 150mm x 150mm.
I used 18mm plywood for the sides and 9mm plywood for the top and the bottom. Everything is glued and screwed together except for the lid. The lid is held into place by two strips of wood that are glued on the inside of the lid to prevent it from sliding open. A heavy roof tile is put on top to prevent it from blowing off and to protect it against the rain.
On one of the boxes that I build, I added a 'landing pad' for the bumble bees so that they don't have to fly directly into the hole.
Last thing to do is to cover the ventilation holes with some sort of very fine mesh to prevent the bumblebees from using it as a 'door' and to prevent other animals like ants and wax-moths to come inside. Make sure to fix it properly as bumble bees are very strong. The first queen that I added pushed the mesh away and escaped.
To give the bumblebees an orientation point, you can paint the entrance around the opening in a bright color. Bumble bees are especially attracted to blue, but can't see a lot of red so that's something to keep in mind.
Step 2: Perparing the box for the Bumble bees
Bumble bees are not very clean and soil their own nests, so you should start with a layer of stuff that is easely cleaned out after bumble bee season. Things like woodchips (the kind you use for your pet rabbit) or rockwool will do or if you like you can add an extra card bord box inside.
On top of this you provide the nesting materials like, old leaves, finely chopped hay, dried mos, upholsterers wadding, kapok,... Stay away from long fibred synthetic substances as they might strangle your bees.
If you find an old mouse nest, then you should add that too. Because bumblebees seem to be attracted to the smell of these nests and they prefer it as nesting material.
You can add some food as a welcome gift for the queen in the vestibule of your box. A little bit of sugar water is ideal. Mix a 1:1 ratio of sugar with water until the sugar is completely dissolved (heating it might help). Some people like to use honey dissolved in water. That's fine but when you use honey you will have to replace the food every 2 days as honey starts to ferment after a few days.
Place your food in a shallow container, like a bottlecap or a Lego brick.
Step 3: Placing the Box
Don't place the box directly onto the ground as moisture will rise into the wood. Put it on a couple of bricks or on a log.
Step 4: Waiting or catching?
The second way is to catch the queen yourself and to place her in the box. Look out for queens that are searching for nests. You will recognize them because they will fly around, entering every hole in the ground they encounter. Bumblebees with pollen on their hind legs might already have a nest so leave those alone.
If you catch a queen, then make sure that there is food in the nest. Because you don't know how much she carries with her. Put the queen in the nest and plug the hole with some moss or some paper. Don't plug it too tightly, the queen must be able to push the plug out herself if she rejects the nest. Mind you: bumblebees are quite strong animals, so they can push out the plug easily. If the plug isn't removed after a few hours then there is a chance that she accepted the nest. In that case you should remove the plug yourself and check the nest after a week to see whether she is still there or not.
Step 5: Ants and waxmoths
Ants are after the honey in the nest and can spell dissaster in the early stages of you population, because they take away the food and kill the larva. To prevent ants from coming in you can create a water-lock. Place your nest on a dry spot in a pool of water and the ants won't get in.
Wax-moths are an even bigger problem. The moth will try to enter the nest and deposit some eggs there. The eggs will hatch and their larva will spin the nest in and eat all the wax inside the nest. This will destroy the nest in no-time. Best solution then is to destroy the whole wax-moths nest, to remove all those larva and to clean your nestbox inside out.
There are, on the web, lots of designs for special doors that will keep the wax-moths out. So if you want to keep them out, then you can try and build one yourself.