Why Do Ants Bump Into Each Other?

Ants touch each other head-on to identify and cooperate with other ants from their colonies. When two ants collide, they smell each other thoroughly to make sure that they belong to the same colony. Ants are surprisingly good at identifying intruders, thanks to their olfactory system, which can immediately tell the scent left by an intruder from the scent of one of their own.

Another theory is that ants touch every other ant coming from the opposite direction to transfer food from one member to another in the same colony/community. This practice is called trophallaxis and is commonly observed in insects like ants, wasps, termites, etc.