Ants are social insects. Many ant species go out of their nests in groups in search of food. Initially, a few worker ants, called scouts, go out of the nest in search of food. Once an abundant source of food is found to the nest, it presses its abdomen to the ground and at frequent intervals extrudes its sting, the tip of which is drawn lightly over the ground surface, much like a pen drawing a thin line.
As the sting touches the surface, a volatile chemical (trail pheromone), flows out of a gland (Dufour’s gland), associated with the sting. In this way the worker draws an invisible chemical line from the source of food to the nest. As soon as it returns to the nest, it contacts a couple of workers, antennates them and makes quick looping movements on the line for short distances. This excited movement attracts the attention of more workers and they start following the scout, which leads, initially, to the food. These workers return to the nest with more samples, and reinforce the chemical line while returning.
This results in recruitment of more and more workers and soon one will find a never ending line of ants moving up and down the line bringing back food. Since the chemical is highly volatile, the trait remains only for a short time. Hence, all the worker ants constantly draw the line over and over again.