Abstract: Elva J.H. Robinson, Duncan Jackson, Mike Holcombe & Francis L.W. Ratnieks Dr. Elva J. H. Robinson (contact author), Ant Lab, School of Biological Sciences, University of Bristol, Bristol BS8 1UG, United Kingdom. E-mail: elva.robinson@bristol.ac.uk Dr. Duncan Jackson, Prof. Dr. Mike Holcombe, Department of Computer Science, University of Sheffield, Sheffield, S1 4DP, United Kingdom. Prof. Dr. Francis L.W. Ratnieks, Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom. Myrmecol. News 10: 120 Insect societies are complex systems which face the challenge of co-ordinating the activities of their many individuals. Ant trail pheromones increase system performance by attracting foragers to rewarding sections of the colony's trail network. Previous work on social insect foraging has focused on the role of these positive, attractive pheromones. Computer simulation studies indicate that the effectiveness of foraging trail networks could be greatly improved by repellent or negative pheromones (Stickland & al. 1999). If…