I have various holes in my house brickwork and have noticed small to tiny bees using them. Tanya Weaver http://www.girlmeetsbee.blogspot.co.uk/ mentioned these are solitary bees, and make homes in all sorts of places, this was my attempt to give them a nice place to live. It could do with a rain cover and maybe the entrance pointing 20 degrees down. Design by RichRap - www.richrap.comPrint with Hexagon Infill and stop at whatever height you like before the top prints Giving you a nice little house for bees. Experiment with different levels of infill but around 8% to 20% seem to give a good size. You can print many and at different heights, their is a middle section and you could print ones to go all around it.