  Using a simple model for the trail formation of ants, the relation between
i)the schedule of feeding which represents the unsteady natural environment,
ii)emerging patterns of trails connecting a nest with food resources, and
iii)the foraging efficiency is studied. Simulations and a simple analysis show
that the emergent trail pattern flexibly varies depending on the feeding
schedule by which ants can make an efficient foraging according to the
underlying unsteady environment.
