Thank you to all who contributed and answered my question in various forms. I did in fact, finally, remember where I had seen the Eckert reference and found the information I required. I was after, in fact, a 'scare' distance. I need to refer to the maximum distance that bees had been known to fly to forage, rather than an *effective* distance beyond which it is unlikely they would forage efficiently. It related to the distance from beehives that pest control officers were to place a substance that was (1) poisonous to bees and (2) attractive to bees. We had previously quoted the 3-5 km as being a 'normally expected' foraging distance, but wanted also to give an extreme that could be substantiated. As for those extreme distances, I have always quoted some mythical person who referred to bees ability to know distance to source, quantity of source and quality (sugar content) and that bees were able to 'put these together' to know if a particular source was (net) better than another and whether a source was (net) better than just staying home (does it cost more energy to fly there and back than is brought back?). Again, thank you for assisting me - I found the answers informative and interesting. ------------------------------------- Nick Wallingford Bay of Plenty Polytechnic (East coast, N Island, New Zealand) Internet [log in to unmask] -------------------------------------