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File photo. Photo: iStockphoto
File photo. Photo: iStockphoto

Left-leaning ants

A particular species of ant, Temnothorax albipennis, when faced with a choice, choose left rather than right

As regular readers of this column know, I like ants. (Also cicadas and bees). Or at any rate, the scientific lessons we can learn from ants. In the past, I have written about a pheromone dead ants release (Dead Ant! Dead Ant!) and how they accurately estimate distance (The Ants Go Marching). They even figured in a set of puzzles (Ropes, Digits and Ants). So, you can imagine my delight when I found some new ant research to write about.

But first, a bit about mazes. Not that I imagine readers of this column regularly need to escape from mazes, I’m sure. Still, no doubt you have heard about one simple technique to find your way out of nearly any maze: put one hand on the wall—any wall—and start walking, never removing your hand.

Eventually, you will be outside. You may not have followed the quickest path to the outside. But with what are known as “simply-connected" mazes, this technique is guaranteed to work. In fact, it can be proved mathematically.

There are other techniques. For example, you walk down the passage you are currently in until you come to a fork. There, you choose randomly which way to turn—or choose the same direction every time—and walk down that next passage. It’s a slow, perhaps stupid way to tackle the maze, but it too will eventually get you out.

All right: what if you set an ant down in the middle of a maze? Lacking a hand to place on a wall, it could choose to follow a wall anyway. Then again, you’d think it’s more likely that it would follow the second technique above: choose randomly when it arrives at a junction. After all, ants don’t have much intelligence. Or do they?

Well, perhaps it’s true that ants probably don’t have the intelligence to work out a better way to escape from the maze. It’s not clear they even understand that they’re trapped inside one. They just scurry along, choosing directions at random when they need to.

Except that there’s now evidence that their behaviour is not quite as random as we might believe.

In 2014, researchers at Bristol University’s Ant Laboratory—which I have immediately added to my bucket list of places to visit—published their findings about how a particular species of ant, Temnothorax albipennis, explores “unknown nest sites". Here’s what they found: the ants turn left.

More accurately, they “show a leftward turning bias" in such exploration. That is, most of the time, they turn left.

One thing I found intriguing about this paper is that it says this bias “is initially obscured by thigmotaxis (wall-following) behaviour". So, these ants do follow walls; in fact, by actually touching them (thigmotaxis refers to the motion of an organism in response to touch). But if you study them enough and collect enough data on their movements—as these researchers did—you realize that the majority of these scurrying creatures, when faced with a choice, choose left rather than right.

Why? Other researchers have noticed that when they get into fights, several species of ants tend to get injured more frequently on their left sides. Also, when they are alarmed, ants tend to turn left. These two patterns suggest that ants use their left eyes for “vigilance and readiness for rapid response"; that is, to watch out for dangers such as enemies or predators.

If true, this would encourage left turns in unfamiliar situations. So perhaps that’s one factor at work here.

But when Temnothorax albipennis ants go out exploring, says the paper, they “need to investigate rock cavities that are typically dark, narrow and partly maze-like, and thus scouts exploring such spaces require a reliable method to ensure that they find their way back to the entrance".

Anything that will make this task easier helps. So, a simple instinct to turn in one direction—left, in this case—“mitigates the cognitive demand on ants confronted with repeated decision-making". And there’s one more angle to all this. If the whole colony shares this instinct to turn left, “subsequent scouts entering the same maze would be more likely to encounter their nest-mates".

That’s useful. As we all know, when you find yourself in unknown and possibly threatening circumstances, there’s safety in numbers. How comforting to know instinctively that you will probably bump into your pals who have gone before you.

The Bristol researchers make a final point with their findings. In species that tend to be solitary, they point out, there are inherent risks in using only one eye to look for predators, or in “stereotypical behaviour" like turning left. The predator could easily choose to attack from the right, after all, and find advantage that way.

But ants are eusocial animals, meaning individuals cooperate in their various tasks. The benefits of such “coordinated behaviour" more than compensate for individual risks. Thus, when you look at an entire colony of these ants, you notice “the emergence of a population-level turning asymmetry".

Which is one excellent way to describe left-leaning ants.

Once a computer scientist, Dilip D’Souza now lives in Mumbai and writes for his dinners. A Matter of Numbers explores the joy of mathematics, with occasional forays into other sciences.

Comments are welcome at dilip@livemint.com. To read Dilip D’Souza’s previous columns, go to www.livemint.com/dilipdsouza

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