Free living honey bees in a chimney in Switzerland, near Zürich. The bees were first noticed in 2012, and the nest has always been occupied (2020). As the bees always have flown in early spring, we believe, that they have survived for many years. Regular swarms have been observed around May - June, showing the successful reproduction of the colony.
You can read more here: https://freethebees.ch/blog/2020/10/06/freethebees-bulletin-nr-16/ and page 8
14 Aug 2020