When a sweet morsel falls on the ground, how do ants converge on it?
Gaurav Garg, Gurgaon, Haryana
Ants are social insects, meaning that they live in colonies with group integration, division of labour and overlap of generations. Since they have the division of labour, worker ants have the foragers who collect the food for the colony. Few foragers who are best known as ‘scout ants’ randomly wander around to search for the food in various directions from the colony.
Various food materials including the sweet morsel has a specific odour. Most of the ant species have the capacity to sense and differentiate a wide variety of odours from various food sources. This is possible for most insects including ants because of the presence of olfactory (chemosensory) neurons in the hair-like sensilla located primarily on the antennae.
Thus the wandering scout ants smell the sweet morsel from a distance through chemoreception and approach the food. Once it reaches the food, it takes a food piece and returns to its nest (colony). While returning, it marks the path between the food source and its nest using a chemical substance called ‘trail pheromones’ produced from its abdominal glands.
These trail pheromones are volatile compounds that are perceived by the other foragers of the same colony. Hence most of the foragers from the colony now approach the sweet morsel and while moving, each individual forager leaves the trail pheromone so that the others can follow the path quite easily because of the stronger marking.
This is continued until the food source is exhausted, when the returning forager will not leave any trail pheromone. Soon the trail pheromones evaporate quickly and hence the food path gets faded. Once again, the scout ants start their food hunting.
DR. R. SRINIVASAN, Entomologist and Head of Entomology Group, AVRDC-The World Vegetable Center, Tainan, Taiwan
