Red Mason bees (Osmia Rufa).
To aid pollination of our orchards, we use Mason Bees.
These are very docile, and do not create honey. They only gather pollen and mud.
They lay eggs in hollows in walls etc. Then they add a quantity of pollen, for the newly hatched to feed upon in spring.
When each egg has been laid and sufficient pollen has been added. The hole in the wall is plugged with mud. If the depth of the hole is deep more eggs are laid and plugged, until the hole is full.
We use tubes as an alternative to a hole in the wall. Strangely the first eggs laid in the holes are female, followed then by a few males. The males are the 1st to hatch.