How ants optimise food search decoded

Ants are capable of complex problem-solving strategies that could be widely applied as optimisation techniques, scientists say.

PTI| Last Updated: May 27, 2014, 18:27 PM IST

Berlin: Ants are capable of complex problem-solving strategies that could be widely applied as optimisation techniques, scientists say.

Understanding the ants could help analyse similar phenomena - for instance how humans roam in the internet.

An individual ant searching for food walks in random ways yet the collective foraging behaviour of ants goes well beyond that, as a new mathematical study shows the animal movements at a certain point change from chaos to order. This happens in a surprisingly efficient self-organised way.

"Ants have a nest so they need something like a strategy to bring home the food they find," said lead-author Lixiang Li from the Potsdam Institute for Climate Impact Research (PIK).

"We argue that this is a factor, largely underestimated so far, that actually determines their behaviour," said Li.
The research team basically put almost everything that is known about the foraging of ants into equations and algorithms and fed this into their computers.

They assume that there are three stages of the complex feed-search movements of an ant colony:
Initially, scout ants indeed circle around in a seemingly chaotic way. When exhausted, they go back to the nest to eat and rest.

However, when one of them finds some food in the vicinity of the colony, it takes a tiny piece of it to the nest, leaving a trail of a scent-emanating substance called pheromones.

Other ants will follow that trail to find the food and bring some of it home. Their orchestration is still weak because there is so little pheromone on the trail.
Due to their large number, the ants go lots of different ways to the food source and back to the nest, leaving again trails of scent.

This eventually leads to an optimisation of the path: Since pheromones are evaporative, the scent is the stronger the shorter the trail is ? so more ants follow the shortest trail, again leaving scent marks.
This generates a self-reinforcing effect of efficiency ? the ants waste a lot less time and energy than they would in continued chaotic foraging.

The study appears in the journal PNAS.