Stem discs are unsuitable as all their fibres and water conduit elements are cut. In damp weather, these fibres attract air moisture - their original function was for water transportation - and the wood swells up. These tensions lead to cracks building up. With untreated wood, parallel passages are drilled into the lengthwise timbers. An interval of 2cm is kept between the drill holes to prevent cracks. The fibres across the hole openings are removed with sandpaper.
Placing the drill holes symmetrically makes it harder for the bees to orientate themselves when flying in. As they orientate themselves optically, finding the right entrance to the nest is not easy with the unnaturally high stock density that comes with a nesting aid. Therefore, creative models have been devised.
¥ Hollow plant stems: Bamboo, reeds
These are cut into pieces. The inner diameter should be 2-9mm, as anything over 1cm is unsuitable. The insects will settle in stems which are closed at one end, or have a straight surface at their backs. They are bundled together with wire, twine or cable ties and placed in the holes of perforated tiles or stones, or housed in tins. The stems are densely packed in order to prevent any of them from falling out, and protected from birds by a wire at the front end.