Formation of trails and exploration networks by ants
Many ant species produce large dendritic networks of trails around their nest. These networks are extremely important for the life of a colony as they channel all the movements of ants searching and retrieving food around the nest. These trail networks result from feedback mechanisms that involve the use of pheromones: chemicals compounds that attract other ants to walk in the same direction.
Observing the formation of trail networks in real time
When a colony of Argentine ants (Linepithema humile) is given access to a circular arena, it is possible to observe the formation of one such network in controlled experimental conditions (see the image on the right, showing the evolution of the trail network over one hour from the beginning of the experiment; ants enter the arena from the centre).
The scale of the system is convenient for observing easily both the growth of the global pattern and the movement of individual ants. We can hence try to understand with precise quantitative relations how one depends on the other.
Individual rules of response to pheromone
Together with Marjorie Labédan and Simon Garnier I collected a large amount of data on the formation of trail networks with the above setup.
As the arena is not marked with pheromone at the beginning of the trial, we can reconstruct the whole map of pheromone marking at any postion and any time by integrating the number of passages of ants, in a similar way to what is shown in the illustrative video below.
We can then establish a few rules of individual response to pheromone concentrations. These include finding the expected change of direction of ants as a function of pheromone concentrations on their left and right side, or testing how their speed of movement depends on the amount of pheromone marking etc.