400 paper tubes without plastic plugs.
The paper tubes where only designed for the mason bee breeding and and were used by both mason bee species. The tubes become bundled and attached on the specific spot, ideally close to other nesting sites and necessarily protected from rain.
The mason bees only accept the tubes, if they are closed on one side. Either with plugs of some kind or attaching the tubes tight to a back wall.
Dimensions: 7,5 or 9 mm x 150 mm