Though I have not done open feeding, the fact that it can set off robbing in an apiary has always left me wondering just how the robbing gets started. I assume it starts out as a foray by foragers, who then recruit more. But, what "signal" is it that the robbers are responding to? Is it because in open feeding the bees will leave traces of syrup on the landing board that are detected by other bees, similar to what can happen with a Boardman feeder, or is there more to it? Are there other signs that come from a hive that is feeding that might draw robbers during a dearth?