Recruitment Strategies and Foraging Patterns of Ants: What Shapes Them and Why?

The effectiveness of procuring food by any ant colony depends upon the strategies adopted while recruiting the foragers to fetch food and the geometry of paths that these recruited foragers employ for searching and harvesting the food. This paper analyzes these recruitment strategies and search paths adopted by ants, and attempts a synthesis of the possible evolutionary process shaping them. Ants exhibit a wide range of recruitment strategies that differ in the size of the foraging team and the interactions among its members. It is shown that these diverse strategies are strongly associated with the size of the ant colony. Small colonies recruit individual foragers, while large colonies recruit foragers en mass; moderate size colonies exhibit a mix of these strategies. This association between the colony size and foraging group is argued to be a consequence of the crisis in processing information in large colonies. While in small colonies, collective decisions to recruit individuals (and small groups) can be easily arrived at, by the ants at the colony level, in large colonies, the tsunami of information flow in space and time creates a crisis for integrating and processing the data. As a result, the task of recruitment is inevitably shifted from the nest level to the foraging paths where individuals are entrusted to self-recruit based on the information gathered by them; this leads to a seamless and spatially dynamic recruitment of workers resulting in an en mass foraging strategy. Further, the size of the recruited team is also shown to be shaping the geometry of the foraging paths. While individual foragers search and harvest food in a circular or sinusoidal movement pattern, the en mass foragers adopt trails or columns that grow and branch out in a bifurcating system. These foraging paths adopted by different group sizes are shown to be very effective in ‘managing’ the complex substrates they forage on, and also to be very efficient in maximizing the benefit-to-cost ratios of foraging.