If you see your bees making this "horseshoe" pattern on the front of the hive, you are being forewarned that they will swarm soon, according to Ormond and Harry Aebi, beekeepers and authors of the book, Mastering the Art of Beekeeping, published by Unity Press, Santa Cruz, Calif. 95065.
The Aebis have observed that bees will give this signal three days before they begin to build queen cells. Bees will crawl up the front of the hive and veer toward the right while an equal number will crawl up and veer toward the left, then crawl down to the entrance again. They will repeat this pattern as long as the sun is shining.
If you do not want that hive to swarm, you have about three days in which to relieve the congestion with additional supers. Otherwise, the Aebis say, a swarm will emerge in approximately three weeks.
Organic Gardening, September, 1979