This is a hand made product from re-purposed wood. And becasue of this, somtimes each home might vary from one another.
 
Link to a video of them being made:
https://youtu.be/0d05T3ngA-Y
 
HOW SOLITARY BEES NEST: The female deposits eggs in the tubular holes in the wood. The bee will seal each egg typically with mud and saliva to form a waterproof cacoon with layers of pollen loaf for after the egg hatches into a larva to eat as food. The larva will contiue to eat unitl spring and begin to pupate and form into a a full grown bee. Male bees typically emarge first to wait for the females so they can mate and fertilize the females so the cycle can start again.