AllaFourmis: How ants can explore a new environment ?

This is the story of our final one-week project. It all started from this video we saw on youtube. From that, we wondered how sensible were ants to magnetic fields, and found this article.

The question we decided to enquire on during this week was thus “What factors determine how an ant choses to explore its environment”.

What we know of ants is that they leave chemical messages for their  peers, called pheromones, and those inform the other ants of what direction they took and what they found there. The more ants go that way, the more the pheromone trail intensifies, and the more ants are likely to go that way as well.

But what if there are no pheromones in the first place? what influences the first decisions?

This is what we decided to test this week, and in two ways: By the presence of another specie’s pheromone, and by the orientation of the environment’s magnetic field.

Thanks to some master students, we got two species of ants: Messor sancta and fire ants. We placed four boxes of 30 messor in a device that trained them to get food only from one direction in the magnetic field, which was supposed to get them used to orient following this field. We let them get this habit for two whole days before switching the magnetic field and testing to see if they naturally went the other way.

During that time, we did experiments on another way that could influence how ants explore its environment.  

Each ants’ species have their own pheromone but we asked ourselves if one species could recognize another ants’ pheromone. Our two species never interact naturally because they are geographically separated. So there are they are not “friend nor enemies”.

Basically we put next to each species’ anthill some tubes in which they would go and leave a pheromone trail.

Schema of the pheromones experiments

After 1 hours one of the paths was covered with pheromone and other was not. After this we exchanged the tubes to see how the ant’s reacted to the other specie’s scent. At the intersection of the tube, The ants had to choose between the two paths to find food. To see which way the ants went in each tube ( left or right ) we built a motion sensor that we put around the tubes. Of course we could use our eyes but as we did many long experiments we had to find a way to automate the ant’s detection.

Our boxes-sensors put on our tubes

We thus built a box in which we placed a LED (light-emitting diode) and a LDR ( light-dependent resistor). The principle is simple. As the ants pass through the tube, they go between the LED and the LDR. It then blocks some of the light and the LDR detects the light intensity difference. With an arduino code we are able to see the decrease of luminosity caused by the passing of ants.

The same apparatus was used to detect the ant’s decision in the magnetic field experiment, and we could clearly see which path they chose.

So what did we found out?

Well it appears that the ants tend to follow the food pheromone trail no matter who left it ! They mostly went in the tube where the other specie had left a trail. Incredible, isn’t it?

Graphs that we have obtened for magnetic experiment

For the magnetic field, the ants did not choose a particular path, and went in both tubes in equal proportions. So either the messor sancta are not reactive to magnetic field, or they just did not stay there long enough to get used to orient in function of the magnetic field.

The device for magnetic experiment

By Anne-Pia Marty, Louis Gallard, Léon Grillet et Amélie Bouissou

References:

• http://www.sciencesetavenir.fr/
• J.B. Anderson, R.K. Vander Meer, Magnetic orientation in the fire ant, Solenopsis invicta, Nature, dec 1993.
• Alexander N. Banks and Robert B. Srygley Orientation by magnetic field in leaf-cutter ants, Atta colombica (Hymenoptera: Formicidae) international journal of behavioral biology, oct 2003
• Yilmaz camlitepe, David J. Stradling Wood Ants Orient to Magnetic Fields, the royal society biological sciences Published 22 July 1995.
• Fernando J. Guerrieri, Volker Nehring, Charlotte G. Jørgensen, John Nielsen, C. Giovanni Galizia, Patrizia d'Ettorre, Ants recognise foes not friends, Proceedings of the royal society, biological sciences, May 2009
• Vincent Fourcassié, Audrey Dussutour, Jean-Louis Deneubourg, Ant traffic rules, Journal of Experimental Biology 2010 213: 2357-2363; doi: 10.1242/jeb.031237
• Andreas Simon Brandstaetter, Annett Endler, Christoph Joannes Kleineidam, Nestmate recognition in ants is possible without tactile interaction, Nature, july 2008.