In Drosophila melanogaster food search behaviour, groups of flies swarm around and aggregate on patches of food. We wondered whether flies explore their environment in a cooperative way as interactions between individual flies within a population might influence the flies' ability to locate food sources. We have shown that the food search behavior in the fruit fly Drosophila is a two-step process. Firstly, 'primer' flies search the environment and randomly land on different food patches. Secondly, the remaining group of flies move to the most favorable food source and aggregate there. We call this a 'search-aggregation' cycle. Our data demonstrate that flies do not individually assess all available food resources. Rather, social interactions between flies appear to affect their choice of a specific food patch. A genetic analysis of this 'search-aggregation' behavior shows that flies carrying mutations in specific genes (for example, the dunce (dnc) gene which codes for a phosphodiesterase) were defective in this search-aggregation behavior when compared to normal flies. Future investigations of the neuronal signaling involved in this behavior will help us to understand the complexities of this aspect of Drosophila social behaviour.