First, I find it quite normal to get extra activity at the hive entrance when sugar syrup is introduced. If the hive is new, and has not been fed before, the bees may be quite hungry, and therefore the new food gets them going. I watched a hive near starvation come back to life almost immediately when sugar syrup was introduced. Next, if the hive is a swarm, they don't have any food with them for a long stay, and if the weather has been bad, then the food again is probably just getting them back to be active. I doubt seriously if robber bees are the cause of the extra activity. I am feeding a weak swarm, we've had lots of rain in our area, and the other hives are ignoring the whole thing, they are too intent on real nectar. Hope you are medicating the bees, if you don't expect honey from them this summer, medicate and use apistan to keep them healthy. Next year there will be a strong hive. 0000,0000,ffffW. J. Fernihough (Bill, [log in to unmask] Engineer, Beekeeper, Computer Nerd ffff,0000,0000All things cometh to he who waiteth if he worketh like hell while he waiteth.