It is mid-March now and this is the moment, here in the Netherlands, that the bumblebee queens are coming out of hibernation. You can easily recognize them, because they are the only bumble bees flying out there for the moment. All bumblebees die in autumn each year, with the exception of the new queens who go into hibernation till the next spring.
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 can be held in a very wide range of nest boxes, made out a lot of materials. You can keep them in a buried flowerpot or teapot, a cardboard box, stone box or styrofoam box, and many more. I will show you how to build just one type of wooden box here. If you are interested in the other types of boxes, then you'll find lots of designs on the internet.
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.