Thursday, January 21, 2010

Humanizing ants

E.O.Wilson has a fictional story, Trailhead, about a colony of ants in this week's New Yorker. This is a phenomenal way of learning about about the behaviour of ants (oh and please relax about anthropomorphism in the story - we have now seen enough Pixar films to be upset about this). But perhaps more importantly for us, here is a great example of cooperation among the members of its own species. This is a gripping tale of the rise and fall of the Trailhead ant colony. Here is the beginning of the story, and then later I have two more bits to highlight. But if you have time, do read the full story:
The Trailhead Queen was dead. At first, there was no overt sign that her long life was ending: no fever, no spasms, no farewells. She simply sat on the floor of the royal chamber and died. As in life, her body was prone and immobile, her legs and antennae relaxed. Her stillness alone failed to give warning to her daughters that a catastrophe had occurred for all of them. She lay there, in fact, as though nothing had happened. She had become a perfect statue of herself. While humans and other vertebrates have an internal skeleton surrounded by soft tissue that quickly rots away, ants are encased in an external skeleton; their soft tissues shrivel into dry threads and lumps, but their exoskeletons remain, a knight’s armor fully intact long after the knight is gone. Hence the workers were at first unaware of their mother’s death. Her quietude said nothing, and the odors of her life, still rising from her, signalled, I remain among you. She smelled alive.
And here is a nice description of the colony a superorganism and examples of cooperation between ants. And, yes, the queen can live for upto 20 years!

As the months passed, the Queen, growing heavy with egg-filled ovaries, retreated ever deeper into the earth, distancing herself from the still dangerous nest exterior. She had become an extreme specialist: she laid eggs, while the workers performed all the labor necessary to raise her offspring, their sisters. They were the Queen’s hands and feet and jaws, and increasingly they replaced her brain. They functioned together as a well-organized whole, dividing up the tasks without regard to their own welfare. The Trailhead Colony began to resemble a large, diffuse organism. In a word, it became a superorganism.

By the time the colony had reached its full mature size, two years after the nuptial flight of the Queen, it contained more than ten thousand workers. It was able, in the following year, to rear virgin queens, and males, and through them to give birth to new colonies. By that time the Queen was producing eggs at the average rate of one every fifteen minutes. Heavy and torpid, she lay in the royal chamber at the bottom of the subterranean nest, five feet below the surface, a distance of four hundred ant lengths. By human scale, the ant city was the equivalent of two hundred underground stories. The mound of excavated soil capping the nest added another fifty stories aboveground.

The Queen may not have been the leader of this miniature civilization, but she was the fountainhead of all its energies and growth, the key to its success or failure. The metronomic pumping out of fertilized eggs from her twenty ovaries was the heartbeat of the colony. The ultimate purpose of all the workers’ labor—their careful construction of the nest, their readiness to risk their lives in daily searches for food, their suicidal defense of the nest entrance—was that she continue to create more altruistic workers like themselves. One worker, or a thousand workers, could die and the colony would go on, repairing itself as needed. But the failure of the Queen would be fatal.

Now, after twenty more years, the catastrophe had occurred. The death of the Queen was the greatest challenge the colony had faced since the days of its founding.

The story goes on describing the various aspects of the colony, but what was fascinating to me was the description of how ants get rid of corpses and how they act past the queen's death:

Within a week, the constant licking of the royal corpse in the Trailhead Colony began to break it into pieces. The pheromones that had bonded the Queen to the workers now hastened her funeral. One by one, the fragments, reeking of oleic compounds, were carried out of the royal chamber. Unknowingly, the ants bade farewell to their mother. No ceremony was performed. Instead the workers bearing the body parts wandered alone through the nest galleries in search of the Trailhead cemetery. This place had no special shape, nor did it contain any token of remembrance, even for a queen. It was merely a chamber at the periphery of the underground nest. The ants dumped all kinds of debris into it, including discarded cocoons shed by newly emerged adults, inedible pieces of prey, and deceased colony members. When the corpse carriers came close to the refuse chamber, they turned their burdens over to cemetery workers. These specialists were ants who constantly rearranged and added to the refuse piles. They stayed close to their work and were for the most part avoided by their nest mates.

In cemetery work and all other activities, the guiding principle of the Trailhead Colony was self-sacrifice. The dominance of the colony over its individual members was total. A worker’s life story was programmed to be subordinate to the superorganism’s needs. If a worker died, the colony was weakened to some measurable but relatively inconsequential extent; the deficit could be quickly made up by rearing another worker in the nursery. If, on the other hand, a worker behaved selfishly, consuming for a good part of her life more resources than she contributed, this weakened the colony far more than if she had the decency to desert or die.

The colony’s members had given up the chance to reproduce, at least as long as the Queen was alive and healthy. They willingly accepted tasks—foraging, soldiering—that would almost certainly lead to early death. The sick and the injured did not seek help; they moved on their own to the outermost nest chambers. Dying workers often left the nest completely, thereby avoiding the spread of infectious diseases. Older workers who were healthy but approaching the end of their natural life span also emigrated to the nest perimeter. From there, they often became foragers, exposing themselves to a much higher risk from enemies. When defending the nest, the elders were among the most suicidally aggressive. They were obedient to a simple truth that separates our two species: humans send their young men to war; ants send their old ladies.


Lina Malkawi said...

Very creative. I never knew E.O. Wilson wrote fiction. Seems like there isn't an educational method he hasn't used in order to educate, inspire and motive.

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