Our top-bar hive has been sitting in the yard vacant ever since our package absconded from it this time last year.  I've been leery of giving the structure another try because the Warre hive is working so well, but reading Swarm Traps and Bait Hives suggested another possible use for the top-bar hive --- catching swarms.

The first step in the top-bar-to-swarm-hive conversion involved looking inside and cleaning the hive up.  In the process, I discovered that our top-bar hive wasn't entirely vacant after all.  An ant colony was living in one corner, a wasp had laid eggs in a new paper nest, and what appeared to be a mouse nest covered most of the hive's bottom.  Once I pulled out the "mouse nest," though, I discovered that it was actually a bird nest, perhaps from the miniscule Blue-gray Gnatcatchers that make such a racket around the edges of our yard in the spring.  There were no eggs present in the bird nest, so I figured it was okay to make the birds find a new home, and I had no qualms about doing the same for the wasp.  (I left the ants alone since it seems like bees and ants can coexist.)

Next, I considered the cavity size of the top-bar hive.  The instructions I'd read last year recommended moving the follower boards in so that only twelve top bars were included in the bees' initial living area.  However, my calculations suggest that leaves a cavity volume of only 29 liters, while 40 liters is the optimal size bees look for when choosing a new home.  So I moved the follower boards to the ends of the hive and doubled the interior space.

One hypothesis about why our bees absconded last year was that the hive was getting too hot in the sun, so Mark put in a max-min thermometer to see what temperatures the colony would have been dealing with.  Swarm Traps and Bait Hives recommends locating these structures in full shade for best chances of catching bees, and more shade does seem to be merited since the top-bar hive reached 110 Fahrenheit last year.  We may move the structure elsewhere now that it's been reinvisioned as a swarm trap.

Finally, I smeared some lemon balm around the inside of the top-bar hive.  My lemongrass oil hasn't arrive in the mail yet, but my gut says lemon balm will work just as well as a swarm attracter.  We'll just have to wait and see.