Ants are social insects, which means they live in large colonies or groups. An ant has eyes that allow them to see extremely well because of the many lenses. Ants also use chemicals called pheromones to leave scent trails for other ants to follow. When the visual information and the chemical information are contradictory, to which information does an ant give priority? In the present study, we study on the selection of the foraging path of garden ant, genus Lasius, which can recognize and response to both visual information and chemical information. Specifically, by setting un-optimized initial pheromone path that connects the nest to a feeding site with one corner of finite angles along the path, we made situations such that the optimal foraging path and along-pheromone path are separated from each other. Hence with varying the corner angle and the total path length, we observed whether ants keep initial path or newly develop the optimal path. It was found that for homing ants that got food, a sharp transition from the regime of keeping the initial pheromone path to the regime of developing the optimal path takes place as the relative angle between the direction assingned by the chemical information and that assingned by the visual information exceeds a threshold. Next, it is believed that the trail pheromone has a species-specific structure. F. Kern et al. identified Mellein as a trail pheromone of the ant (Lasius niger) which widely inhabits Europe. Until 2005, the similar kind of ant which inhabits Japan was named Lasius niger. However, recently, the ant has been called Lasius japonicus from the behavioral and the physiological difference. This fact suggests that a new trail pheromone exists to Lasius japonicus. We now wish to report the identification of the multicomponent trail pheromone of Lasius japonicus, which consists of a synergistic mixture of three alkyl ketones. 2-Tridecanone, 2-undecanone and 2-dodecanone are components of the trail pheromone of the garden ant, Lasius japonicus. These ketones were extracted from the rectal fluid of dissected worker ants, and identified by the mass spectra and gas-chromatographic retention times. The same ketones could also be detected in the material excreted by the ants on their foraging path. We believe this identification to be carried out at the lowest level of detection yet achieved for a pheromone, and for it to be the most complex mixture yet identified as an insect trail pheromone.
