Ants Go Marching

At a young age, children in the United States learn — via a common toddler tune — that ants congregate and march, as a horde, toward a common destination.  While this isn’t true for all ants, it is indeed the life of a few hundred species of ant, collectively known as “army ants.”  Army ants are typically nomadic, traversing great distances in search of food before setting up temporary nests, only to move again shortly thereafter.

The main foragers lead the way and emit pheromones — chemical secretions other army ants can detect — in order to give the rest of the clan a trail to follow.  Those ants which can’t detect the pheromones (a situation which commonly happens as armies grow large) simply follow a nearby ant.  This allows for army ant brigades to extend for extraordinary lengths, at times observed to extend a half-mile long.

But what happens when a group of ants loses the pheromone scent?  Who leads?  The answer:  No one.  Or everyone, depending on your perspective.  The ants form an “ant mill” — a continuously rotating circle of ants, each following one another, but going, net, nowhere, as demonstrated in the video below.

The ant mill is, ultimately, fatal, as the ants die of exhaustion.

Bonus fact: One type of army ant, those of the genus Dorylus, are particularly dangerous.   Native primarily to central and east Africa, armies of Dorylus ants can number up to 50,000,000 — that’s 33% larger than the (human) population of California.  By human standards, these columns move slowly, a mere twenty meters each hour, so in most cases, Dorylus are a significant nuisance — but not much else.  However, by sheer force of numbers, Dorylus have been known to overwhelm human victims too young, frail, etc. to move, causing suffocation and eventually, death.

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