[FRIAM] Costa Rican ant colonies

[Hugh Trenchard]

Re: [FRIAM] A Fractal IntroductionI thought this might be of interest to some of you.

When I was in Costa Rica in December I had occasion more than once to observe colonies of tiny ants as they travelled in slightly curving lines up and down walls. These were very small ants, each one not much bigger than a millimeter or two in length. Their small size and the fact they traveled across walls closely together in long lines made them amenable to close observation. Generally, their trajectories appeared to match very nearly the fastest routes from sources of food to unknown destinations. 

The ants traveled to and from a discernable food source - a source which I could usually locate by following their lines, and in fact a couple of times the food was bits of egg I had dropped on my kitchen counter! Their destination in the direction away from the food source was unknown to me, however. 

In observing the ants as they travelled up and down in lines, each individual ant touching all others briefly as they passed each other in their respective up and down lines, I struck upon a hypothesis: 

1. Individual ants tend to travel more slowly than single file groups traveling within touching range of each other. This, faster speed for groups, I speculated, would be due to a "drafting effect" that allowed following ants to save energy in travelling behind leaders and that the groups as a "unit" would on average travel faster than individuals traveling on their own. 

This idea was of course inspired by the faster traveling times which pelotons of cyclists can achieve over traveling times of individuals. Whenever one can observe a human effect in a natural setting it tends to validate the effect as being independent of human psychology and motivations, and so to observe optimization by drafting among ants would be some evidence that the collective optimization of cyclist's speed due to drafting is a universal physical principle. 

In the end my data (rough and incomplete due to eventual boredom in tabulating the figures), which is attached in the pdf file, did not lead me to conclude any faster traveling times among groups of ants. The only thing my data could tell me with any degree of certainty was that it took longer for the ants to travel up the wall than it took them to travel down. This can, it seems, be accounted for by the slowing effect of gravity. 

Basically I would need to take more data over longer distances to see if any conclusions could be drawn about the average times of groups, which still may be true, despite the data I gathered which shows an average of 9.375 seconds for the individual ants traveling down the 11 inches in my observation window, compared to 10.1 seconds for the groups traveling down. 

The reason it may still be true that the groups travel faster on average is that the total number of ants in the "group" data set is much higher than the total number of ants in the "individual" ant data set; data would have to be compared for the same total number of ants, which I did not do. This would need to be done for more conclusive data. 

However, despite a lack of any conclusive evidence of a drafting effect among these ants, it was interesting to see how the two lines of ants involved each ant touching each other as they crossed paths. I came to speculate on a that this touching is a mechanism for optimizing the distance (ie finding the shortest distance) between the food source and the end destination (whatever that was).

It occurred to me that the very reason the ants travel in two lines back and forth, and touching each other as they pass, is to minimize the distances between ants so that nearly random movements end up, by continuous adjustment, establishing nearly the shortest distance between the food and the destination. 

I understand that ants use pheromones to map their routes for each other, but I speculate that ants, or at least this type in particular, also optimize distances by smoothing a trajectory by continuous adjustments and shortening of distances between individual ants as they approach each other in passing. The main thing I am suggesting (which may not be new - I haven't researched the point) is that the two traveling lines serve a purpose other than simply one line consisting of food carriers and the other line consisting of those going to the food to pick up a bite of food and return: ie. in other words there may be many ants who do not pick up food but whose sole purpose in traveling the distance, although of course they don't know it, is to ensure the distances traveled are optimized! 

I thought of a way this could be tested. A group of people, say one hundred of them, all blindfolded, are situated at one end of a field, say 300m long. They cannot see due to their blindfolds, and nor are they allowed to speak to each other, but they can touch each others' backs to know where they are. 

The idea is for the group to begin walking to the other side of the field. When the first person gets there (the point marked by something that can be felt by touch), he or she then turns around and tries to return to the beginning point. In order to find the route back to the other side, that person can touch each of the others who are still making their way to the far end. In turn, each person, as he/she reaches the far side, must turn around and try to return to the exact beginning point. 

Similarly, when (if!) each one has returned to the beginning they must return again to the turning point on the other side, and go back and forth. 

Basically, by touch alone, and not by talking or speaking, I speculate they will eventually, after a lot of bumping and inefficient route taking, establish two smoothly flowing lines where each person touches the other in passing and will find nearly the shortest distance between the two points, even though none of them will know it! 

Obviously I could be wrong, but that is one way to test what I believe to be occurring among the ants. 

Hugh Trenchard




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