yes, it's communication through smell...
Ant communication is accomplished primarily through chemicals
called pheromones. Because most ants spend their time in direct
contact with the ground, these chemical messages are more developed
than in other Hymenopterans. So for instance, when a forager finds
food, she will leave a pheromone trail along the ground on her way
home. In a short time other ants will follow this pheromone trail.
Home is often located through the use of remembered landmarks and
the position of the sun as detected with compound eyes and also by
means of special sky polarization-detecting fibers within the eyes.
Returning home, they reinforce this same trail which in turn
attracts more ants until the food is exhausted, after which the
trail is no longer reinforced and so slowly dissipates. This
behavior helps ants adapt to changes in their environment. When an
established path to a food source is blocked by a new obstacle, the
foragers leave the path to explore new routes. If successful, the
returning ant leaves a new trail marking the shortest route. Since
each ant prefers to follow a path richer in pheromone rather than
poorer, the resulting route is also the shortest available.
Ants make use of pheromones for other purposes as well. A crushed
ant, for example, will emit an alarm pheromone which in high
concentration sends nearby ants into an attack frenzy; and in lower
concentration, merely attracts them. To confuse their enemies,
several ant species even use what are termed propaganda
pheromones.
Like other insects, ants smell with their antennae, which are long
and thin. These are fairly mobile, having a distinct elbow joint
after an elongated first segment; and since they come in
pairs--rather like binocular vision or stereophonic sound
equipment--they provide information about direction as well as
intensity. Pheromones are also exchanged as compounds mixed with
food and passed in trophallaxis, giving the ants information about
one another's health and nutrition. Ants can also detect what task
group (e.g. foraging or nest maintenance) to which other ants
belong. Of special note, the queen produces a certain pheromone
without which the workers would begin raising new queens.
Some ants also produce sounds by stridulation using the gaster
segments and also using their mandibles. They may serve to
communicate among colony members as well as in interactions with
other species
http://en.wikipedia.org/wiki/Ant
