When I woke up one summer morning, I noticed a string of dashes on my bedroom wall. The line ran from the ceiling to the wall behind my bed and then disappeared under it.
As I watched, I saw one of the dashes move. It was a small red ant walking up the line. Soon, another one followed and then another, till it grew into an army of ants marching up the wall.
I noticed that while walking in a line the ants were cleaning the wall paint underneath them and, in the process, making a path. And there is a very good reason for them walking in a line.
Ants are social insects. They live in big colonies and have a very organised social life. Red ants make their nests inside the walls of our houses. They generally travel large distances in search for food. In absence of any maps or navigation aids, they have to rely on other mechanisms to find their way around.
Scenting their way
As they walk the ants leave behind a scent that they use to trace their way back to their nests just as in the fairy tale Hansel and Gretel, the children left a trail of pebbles to find their way home from the jungle. The scent that the ants leave behind is called pheromone. The ants walk in a line because they follow the scent left behind by the leader.
Test the ants
If you want to test out this fact, use an eraser and rub it across the path that the ants are taking. The ants will stop precisely at the point where you have rubbed off the smell with the eraser. Directionless, they move in all directions.
So the next time you see a single ant crawling chaotically on the floor, you know what it is looking for.