By Peter Morovic

Memory is commonly understood to be the ability to recall something, to repeat a previously executed task, to recognise a previously experienced situation and then act accordingly. This makes memory also key to learning and evolving one’s behaviour. While commonly memory is thought of in the context of a single entity, one can also consider the question of whether memory is something a collective could have? Amazingly, it turns out that ant colonies are one such example of a collective that exhibits behaviour consistent with having memory. They do so by being able to alter the behaviour of individual ants, or the whole colony, based on past events even when these were experienced only by some of them.

For example, ants are able to return to food they previously found, meaning they somehow remember where it was, and are also able to remember how long it took to get there. Some of these memories are relatively short term – on the order of minutes – while others are much longer lasting and, interestingly, appear to be shared. Red wood ant colonies, for example, are able to remember how to return to the same tree, year after year. Furthermore, they can also pass on their memories: for example, when they emerge after winter hibernation, older ants take younger ones along their usual trail towards food to teach them, before dying. [1] What is surprising in such behaviour is that it’s hard to think of there being individual benefit to the older ant from sharing their memory with the younger one, since their life is coming to an end.

To test the notion of ant memory further, in an experiment, [2] hurdles were placed in the way of some groups of ants in their pursuit for food for the colony. The obstacles were overcome by shifting them or walking around them and after a few days of having had to deal with such barriers, the behaviour of the entire colony changes due to the adverse experience, even if it only directly affected a subset of the colony and even once the disturbances stopped, as if the colony, as a whole, learned from the travails of the days before and adapted so as to avoid them. While the impact on some group of ants only ever directly affected some of them, by sharing this information, the whole colony was able to alter its behaviour and benefits and evolves. So, not only do ant colonies appear to have a form of memory, but this memory also seems to be altruistically motivated: sub-groups who, for no individual benefit to themselves, share their experience in order to adapt to the new conditions, such as obstacles, in order to benefit the whole colony.

(via aeon)

[1] Train communication and directional recruitment to food in red wood ants (Formica), Rainer Rosengren and Wilhelm Fortelius, Annales Zoologici Fennici, Vol. 24, No. 2 (1987), pp. 137-146

[2] From division of labor to the collective behavior of social insects, Deborah M. Gordon, Behav Ecol Sociobiol 70, 1101–1108 (2016). https://doi.org/10.1007/s00265-015-2045-3