All information provided is meant for the Netherlands, northwestern Europe. Habitats in other locations may be very different and the information provided here might not be useful for locations outside of northwestern Europe.
The reduction of suitable habitats for bees, butterflies and other insects makes it harder and harder for these animals to find nesting and hibernation locations. Nesting suitability is essential for the survival of these animals. In the past gardens were much more natural. Rivers still had natural edges, dead wood often stayed where it was and there was often large diversity of native plants. Modern gardens however are often almost entirely paved over, and the diversity of plant life has decreased to a monotone select few species and cultivars that are used over and over (Hortensia, Catalpa, Buxus etc.). These changes play a big part in the reduction of bee and butterfly populations in the Netherlands, and many other places. A bee hotel can be placed to prvide more nesting and hibernation locations.
General information on bee hotels
Bee hotels are man-made objects or locations that provide nesting opportunities for solitary bees. It can be made from a wide variety of materials and can have any shape or size. Even objects such as straw roofing or certain walls can be used as bee hotels if these were placed for solitary bees to nest in. It’s important for solitary bees that their food is found close to their nest. The distance solitary bees can fly from their nest varies per species. Bumblebees and honeybees can fly long distances, but they don’t nest in bee hotels. Solitary bees are the ones that nest in bee hotels, and some of these species don’t fly further than a few dozen meters. Solitary bees live alone, and so have to find the nest and provide food for the young all by itself. After mating, the female will lay her eggs in a suitable nesting site, and place pollen with the egg and close the exit. Once the larva is born from the egg, it will eat the pollen to grow, and it will leave the nest to find a mate after it reached adulthood. About 18% of species in the Netherlands make nests above ground, mostly in holes in wood or hollow stems. The larger part of species, 70%, make their nests only in suitable ground locations, so a bee hotel that only consists of wood will not provide a suitable nesting site for most species. About 12% of species can build their nest in both aboveground and underground locations. This is why it’s best to provide a variety of nesting possibilities aboveground and belowground.
A bee hotel that can hang on a wall. It provides a wide variety of nesting locations for many bees, and many hibernation locations for other insects. The holes drilled in the wood are of different lengths and widths, providing nesting to a wider variety of wood-nesting bees. It also has a sand wall mixed with peat, providing a nesting site for ground nesting bee species. There is also a small section filled with snail shells for the few species that exclusively nest in snail houses, although these are more likely to be used by other insects. There are also some rotten logs without holes, several species prefer to make their own nests in this kind of material.
Demands for bee hotels
To create a proper nesting site for bees, a bee hotel should adhere to several points:
Nesting sites should be placed in a sunny location, oriented Southworth. The increased temperature will help the development of the larva.
Rainwater should be able to drain away. Ground nesting locations should be kempt mostly dry to prevent collapsing, by placing roof tiles over it for example. Holes in wood can best be drilled at a slightly upward angle, this way water won’t flow into the hole.
Use peat or clay, mixed with sand, to help strengthen ground nests. This can also be used to create horizontal sand walls. It can also be used to mason walls where there is plenty of crevices between the stones. This will allow solitary bees to nest between the stones.
Holes drilled in wood should be free of splinters. Holes with splinters will cause damage to the bees' wings.
The wider the holes in diameter, the deeper the hole should be. At a diameter of 1,5mm the hole should be about 2cm deep. This increases to a depth of 6cm for a hole with a diameter of 8mm. Holes with a width of 2,5 to 8mm are most in demand by bees. Holes wider than 8mm are not commonly used. Always make sure the holes are only open on one side, don’t drill all the way through.
Use a wide variety of hole sizes in a nest. Solitary bees are picky about their nest site. If a hole is too big or too small they won’t nest it. So the wider the variety of holes the more bee species will be able to use them.
Do not use tropical wood or wood with tears in them. Tears in the wood will increase the chance of infection by parasites.
Bees will clean their nests themselves, it is not needed to clean them by hand.
Bees need water. So try and provide places nearby where bees can drink if needed.
Examples of bee hotels
The most common type of bee hotel is the wooden block with holes drilled into it. Commonly several wooden blocks are stacked on top of each other, but on single, solid block can also be used as long as the holes are the right shape and size. These bees hotels can commonly be bought at any gardening centre and can easily be placed on any wall. As stated before, only 18% of bees specialize in nesting in wood. So not all solitary bees will be helped by this type of bee hotel. A simple but similar type of bee hotel is to place a wooden sleeper vertically in the ground, and drill holes in the side that’s facing south.
Solitairy bees nesting in a sandbank. Video: Margaux Boeraeve
Another type of bee hotel, which is quite suitable and easy to build, is made by stacking pallets. The open sides can be filled with any number of nesting materials such as peat/sand, hollow stems, hollow bamboo, wooden blocks with holes in it etc. Because it’s so cheap and easy to build it can also be a fun project for workshops or classes with children. If the right materials are used this type of bee hotel can be very effective. The bottom of the hotel can even be buried in sand to provide more nesting options for ground nesting bee species.
You can also take this one step further and connect the pallets to wooden poles to form a wall. These can then also be filled with suitable nesting material.
As stated before, peat can be used as an important and effective building material. Even bees that nest aboveground can use peat as a building material. Many underground nesting bees also need a vertical or slanted sand wall in order to nest. For these reason peat is a great choice for building a bee hotel. Bee hotels with peat walls offer great nesting opportunities, especially when combined with wood and roof tiles. Walls made by stacking loose stones, with peat as mason, also provide great nesting opportunities. These insect hotels also don’t need to be obvious, or take up a lot of space. The wall will also form a dry habitat, where specialized plant species can grow as well.