If bees are in the chimney for several days or longer, it becomes difficult to get them out. This is because they will have started building comb, and the queen may have started laying eggs.
Bees are very reluctant to desert a colony with eggs or brood, so any colony removal will be trickier, longer, more laborious and more costly as you need to physically remove the honeycomb containing the eggs and brood and the bees.
If the colony had gone down into the chimney, this is a job few beekeepers will take on.
Hence, if you discover bees in a chimney, or showing interest in a chimney, immediate action is necessary.
Before a swarm moves in, they will send out shout bees looking for suitable places to move in to. If there are only a few bees checking out the chimney, the following things could deter them from selecting your chimney:
1. Block off the chimney from the top.
2. Light a small smokey fire and keep it lit. This will discourage bees from picking your chimney as a nest site.
3. Insert a chimney balloon, bee screen or similar. (Contact a chimney expert in your area for advice but act quickly!)
4. Set up a bait hive close to the chimney to attract the swarm into that instead.
5. Hang mothballs in the chimney (as high as you can ideally from the top).
6. You can also try hanging a rag soaked in selected essential oils. Cinnamon, Rosemary, peppermint, clove, geranium, tea tree or bitter almond oil can work.
7. Place a rag soaked in vinegar in a dish close to where the bees are flying in and out. (Warning: vinegar contains acetic acid which is corrosive and can damage flue liners, bricks and concrete so use extreme caution.)
Once a swarm has moved in, it becomes more difficult to get them out, but some of the above alternatives can work. You can try to smoke them out by keeping a fire lit, or use essential oils, vinegar or mothballs. You can also sprinkle cinnamon into the chimney.
If you do manage to get the bees out, make sure to get your chimney swept in case there is wax or other debris left in that could pose a fire hazard once the chimney is in use.