Bait hive

I put a bait hive onto my bee shed this afternoon during the warm spell. A full size box with two old empty brood frames and four frames with foundation.  I also put a few drops of Lemongrass essential oil into the doorway. PK told me that this will attract swarming bees looking for a new home.  it is a precaution against one of my hives swarming...... I hope to catch them before they go too far.  Eva