Some are extinct already.
This is a NEW method to make bee habitat.
Colony collapse disorder is hard to blame when most bees are solitary!
Thats right, most types of bees live alone.
One big reason that they are disappearing is habitat loss.
This instructable suggests ways to provide solitary bees with brood space and overnight shelter in an attempt to replace some of that lost habitat. So far it is working much better than I expected.
Step 1: Cob and rods and stems and things
I show a couple of the blocks here.
It worked and there are at least 4 types of bees living in the block.
I recently discovered that solitary bees burrow inside old raspberry canes!
So one really easy thing you can do to help the bees is to bundle up old raspberry canes and leave the bundle in a dry south facing location. I am sure the bees will find them, burrow into some and leave some bee babies to hatch out next spring.
Step 2: Cob and bars and stems
Anything hollow or with a pithy middle.