I have been observing this nest for 4-5 years. It is a huge aspen which has been left when the forest has been logged in the 1990's. I noticed the bees when picking mushrooms in autumn 2019. There has been a swarm in the tree every year and usually it survives until early spring and signs of cleansing flight are clear on the snow. However until now they have died every time before spring really starts. This year (2023) is the 1st time that I observe them surviving the winter so cause for celebration !