<<<There are similar questions about queen cups. Are they built before or
after egg is laid? That may be a foolish question!>>

Not foolish, Gareth, but it does suggest you have not been very observant.
Bees start queen cells even though they have no intention of swarming. They
form small cups around the edges of the  combs and then stop. You may see an
egg in the cups which hints at swarming but not necessarily so as sometimes
the eggs just disappear. The bees have changed their minds,  perhaps due to a
change in the weather, a heavy nectar flow or whatever.  Only when you see
larvae in the cells can you be certain that the bees are going to swarm and
you have just a few days  to decide how to stop them. If you want to prevent
swarming (and who doesn't?) there are many ways open to you. I use a variant
of the Demaree method. George Demaree published details of his method well
over one hundred years ago so it has stood the test of time.It will be found
in any good bee book. I have always used it and it is ideal for anyone with a
few hives.

 <<<I do wonder then how she recognises <size> as such. An instinct. We do
know why. It is an instinct but what are the morphological features of the
instinct?>>>
Many, many years ago, at a bee meeting I attended, the lecturer was asked how
does the queen know which egg to lay. He said she used her antennae as
callipers to gauge the width of the cell. He mentioned an experiment where
the flagellum of one antenna was snipped off af'ter which the queen could not
differentiate between the cells and laid her eggs anyhow. It struck me as an
indecisive experiment as probably the removal of half an antenna might itself
throw her off balance.I have never seen this in print and I have read a lot
of books in my time so do not accept  this as truth.
                         Sid P.