  Many insects like ants communicate chemically via chemotaxis. This allows
them to build large trail systems which in many respects are similar to
human-build highway networks. Using a recently proposed stochastic cellular
automaton model we discuss the basic properties of the traffic flow on existing
trails. Surprisingly it is found that in certain regimes the average speed of
the ants can vary non-monotonically with their density. This is in sharp
contrast to highway traffic. The observations can be understood by the
formation of loose clusters, i.e. space regions of enhanced, but not maximal,
density. We also discuss the effect of counterflow on the trails.
