We have already seen the usefulness of what Grasse calls “stigmergy” for the solution of a general type of complex problem by a not-so-complex organism, the Argentine ant. But these ants don't live to solve problems (unlike the numerous robotic and computational ants designed in their image), they solve problems to live – so what happens after the problem, when the food source is depleted? The articulated path is no longer a solution, but an initial condition; the autocatalytic mechanism no longer a bridge, but a prison. Once again, the answer lies between the ants, in the pheromone-ground. When the food disappears, the ants will not emit pheromone and, over time, the pheromone already on the ground will evaporate, leaving them free to explore.
Stigmergy, in this instance, operates as a kind of distributed memory within the landscape, capable of both remembering and forgetting. It suggets that we should not only speak of the ants in isolation (as individuals) or the colony in abstract (as a group of individuals), but instead, of the ant-pheromone pheromone-ground, as a peculiar kind of organism.
Let's consider another example: termites, which Grasse was studying when he coined the term, “stigmergy.” Eugene Marais theorized the existence of an insect “language” based on scent in his study of South African termites, The Soul of the White Ant, years before pheromones were officially discovered. Since then, the process by which termite mounds are constructed has been described in great detail. Briefly, termites place tiny balls of mud near other balls of mud that have high pheromone concentrations and, as a consequence, mounds develop. As the mounds grow, pheromones at the bases evaporate and the termites will bring the mud to the top, driving the height of some mounds upwards of 30 feet and causing adjacent mounds to meet in arches.
The most striking theory presented in The Soul of the White Ant – so striking that Nobel Prize winning writer Maurice Maeterlinck plagiarized it in his book The Life of the White Ant – is that “the termitary is a separate and composite animal in exactly the same way that man is a separate and composite animal. Only the power of locomotion is absent.”i Marais posited workers and soldiers as blood cells, fungus gardens as digestive organs, the queen as brain, and so on. The termitary has much in common with the human body, whose “many vital organs can be looked upon as a community with specialized individuals grouped into organs, the whole community forming the composite animal.”ii To see the degree to which the termite and termitary are fused together, one only needs to puncture the mound and see the workers transport individual grains of sand to the hole, in order to “heal the wound.” The opening causes intense gradients in temperature, humidity, carbon dioxide, and oxygen, a disruption of the termitary's carefully maintained internal atmosphere; the rebuilding is not defensive but, more accurately, corrective. Sensing some problem in the body of the termitary, termites perform the function of an immune system and attack intruders while repairing the breach in order to restore the termitary's equilibrium.
