The message
from Kay contains these words:

Stonework not brickwork - therefore definitely old though repointed
about 15 years ago.

They're not honey bees - how big a colony do bumble bee type things
form?

Some of them can make quite a large nest, but I don't think the cells
are a wax comb. Certainly the ones I've disturbed (accidentally) in the
past have been rather more like loose birds' nests.

I'd google for masonry bees and see if they match, and then find the
answers to your other questions.

--
Rusty
Open the creaking gate to make a horrid.squeak, then lower the foobar.
http://www.users.zetnet.co.uk/hi-fi/