Adventures Among Ants - Mark W. Moffett [111]
Whether the raid is a success or a failure, the return trip is a cinch. The pack is no longer dependent on its leader. The pheromones the workers released to keep themselves together on their outbound journey persist long enough for them to follow home.8 The retreating ants make use of polarized light as well, though. Taking on a Pied Piper role, Howard has managed to delude the ants into turning around and returning the brood to the nest they just raided by shading the advancing column and using a mirror to redirect the sun.
HOW DID SLAVEMAKING BEGIN?
In The Origin of Species, Darwin proposed that the ancestors of slavemakers may have eaten the brood of other ants, much as army ants do today. He suggested that when the booty wasn’t consumed fast enough, some transformed into adult workers that imprinted on their captors and ipso facto became slaves. At first the nascent slavemakers would have relied on their slaves most heavily for jobs that were costly or dangerous, such as foraging and defense. But with their slaves constantly performing all duties out of habit, the slavemakers would have gradually lost their other domestic skills as well, culminating in the modern Amazon ants that will starve to death if there are no slaves to hand them food. Over many generations, the addition to the supply of laborers would have become so valuable, even essential, that predatory raids metamorphosed into slave raids. Darwin saw the raids in effect as a circuitous kind of food search: what was once a foraging enterprise became a quest for individuals that would do the foraging—that is, a fresh batch of slaves.
Today, the most widely accepted conjecture about the origin of slavery in ants holds that the slavemaker ancestors were competitive species that took brood as part of their war booty and then ate it, even though ant brood wasn’t an everyday part of their diet, and some of these occasionally survived to become slaves.9 This idea has gained favor because the groups of ants that most often evolve slavery have been species that fight over territories or other resources rather than the specialist cannibals of other ants. Despite their predatory raids, for example, no army ant species has become a slavemaker.10 Remember the acorn-dwelling Temnothorax that are subject to enslavement by Protomognathus americanus? In territorial battles between their colonies, Temnothorax eat any immatures they seize.11 But on rare occasions, and seemingly by mistake, they will rear one to adulthood. Such an individual will serve as an accidental slave—unless her confused nestmates kill her first. Indeed, the evolution of slavery must have included a suppression of the worker impulse to kill foreigners, thereby allowing would-be slaves to coexist with them.
The honeypot ants of the American Southwest are a territorial species with an aptitude for slavery. They show fascinating ritualized behaviors designed to avoid lethal conflict, engaging in mock fights called tournaments in which ants from different colonies circle one another on tiptoe to try to make themselves look larger. In this so-called stilt walking, they will sometimes climb on pebbles to stand taller than their neighbors, a ploy that anthropologists call tactical deception, which is associated in primates with keen intelligence.12 For species with a modest labor force, ritualized conflict is a reasonable strategy to avoid casualties, though if one side determines that their workers are larger and outnumber the others, they raid the weaker nest, gorge on its brood, and drag back its honey-filled replete workers as slaves.
Slavery evolved in both ant and human societies out of the need for a compliant and manageable labor force to drive their extensive systems of collective production. Ants are concentrated on producing the brood that will be the source of the next generation, and the labor force geared to this