Ever see bees at their hive entrance with their tail ends in the air, fanning their wings like crazy? It looks a little frantic. It isn't. They're giving their sisters directions.
Bees fan to cool the hive, too. But when the tail end is tipped up like that, she's doing something else. In the video above, I have just caught a swarm of bees that was out looking for a new home. I moved them into this cardboard box so I could transport them to a permanent hive in the apiary, and the bees fanning on the top of the box are making sure that the entire swarm knows where they’ve relocated to.
A scent that says "this way home"
Look closely and you'll see a little pale stripe on top of her abdomen, near the tip. That's the Nasonov gland. She opens it and fans her wings to push the scent out into the air behind her.
The scent is a pheromone, a chemical message that animals send to their own kind. This one is a blend of a few compounds, including geraniol and citral. To people it smells faintly lemony. To a bee, it basically means "this way home."
Who follows it
Lost foragers follow the scent back to the entrance. Swarms use it to pull everyone together: when the bees settle into a new home, some of them fan at the doorway to call the rest of the swarm in.
I'll sometimes see a few bees fanning like this if I've discombobulated anyone during a hive check. Bees that got bumped off a frame or took flight need to find their way back, and their sisters light the way.
Why beekeepers use lemongrass
Some beekeepers put lemongrass oil in swarm traps as a lure. It works because lemongrass oil is mostly citral, one of the same compounds in the Nasonov scent. It's not a perfect match, though. Commercial swarm lures blend citral with other parts of the pheromone, like geraniol and nerolic acid, to get closer to the real thing.
No bee left outside
It's just another example of teamwork in the hive: no bee gets left alone outside.
If you teach grades 3-4 or homeschool, I turned this into a classroom lesson called This Way Home. Kids read about the Nasonov gland, label a fanning bee, and run the Scent Race, a class experiment to see whether fanning spreads a scent faster.
With aloha,
Kelli
Sources
Swarm lures: lemongrass oil vs. synthetic Nasonov pheromone, American Bee Journal, April 2017
Synthetic pheromones to attract honeybee swarms, Free, Pickett et al., Journal of Agricultural Science