Here is a perfect example of ants marching in a line. There following a pheromone trail that’s a chemical trail that they lay down to tell the others, rest of the colony where to go. In his case a scout has laid a pheromone trail directly into the wall this is a weep hole let's moisture out of the wall it's supposed to be there but that moist air drawing this colony and every other colony that comes across that pheromone trail directly into the house.
