The floor comes with an aluminium varroa mesh which unlike steel is resistant to oxalic, formic or other acid varroa treatments. The mesh floor is retained by stainless steel screws.
Slots underneath the floor allow the varroa tray (available separately) to be slid out easily for monitoring but hold it in place firmly when required.
experience gained on a large number of hives in different climates confirms that the varroa tray should be left out all year round apart from short priods of monitoring or when housing a swarm - to make it darker in the hive. in very cold areas the tray is sometimes replaced in early spring to aid colony build-up but it should be removed as soon as possible. If in doubt - leave it out!