Major pests in beekeeping
If care isn't taken, mice can be a major problem to the beekeeper. They will readily enter an occupied hive in winter where they will make a nest. They will destroy some of the combs and may cause so much disruption to the colony that it dies. Mice will also make a nest in stored equipment if not made mouse proof.
When bees are active they will deter mice themselves, but when they start to cluster on cold days in the autumn mice will seek entry. Mice are unable to get through a narrow gap of less than 8-9mm, so some physical form of denying them entry works. If you have a deep floor you will need to restrict the entrance in some way. This could be a flat metal mouse guard with holes in as sold by appliance dealers or an entrance block with a shallow entrance. I use shallow floors that prevent entry of mice.
When making entrance blocks or shallow floors a pencil can be used to size the gap, as I have never found a mouse will enter a gap so small. I don't like making mouse guards from queen excluder because a large amount of pollen is scraped off the legs of the bees.
Equipment that is stored needs to be protected, either by putting it in a mouse proof container, or if it is boxes of combs stack the boxes up with no gaps and put a queen excluder top and bottom.
Although equipment may not always cost much it is valuable when you need it and can't use it. The careful beekeeper will make sure that mice aren't a problem.