A few weeks ago we placed a bee box in the garden and wondered whether anything would use it. I've been checking it regularly and today noticed some ants going in and out of the lower holes, hauling what looks like some pupae around. Meanwhile, two different bee species were either investigating the upper holes, or were actually nesting there. They moved so fast into the holes that I couldn't really get a good look. And if they came back out I didn't see them.