Adventures among Ants. Mark W. Moffett
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Thaumatomyrmex worker at Tiputini, Ecuador, using her long-toothed mandibles to hold her bristly millipede prey while she strips off its hairs before eating. These tiny, solitary foragers are notoriously hard to find.
Ants are highly social. They are classified in the order Hymenoptera, as are wasps and bees, and some of these insects, such as the honeybee and the yellow jacket, are highly social as well, as are all the members of another insect group, the termites.4
The smallest known ant colonies, of at most four individuals, are those of the minuscule tropical American ant Thaumatomyrmex.5 Colonies in the tens of millions are typical of some army ants of the African Congo. Supercolonies, like those of the Argentine ant currently battling for exclusive control of southern California, have populations in the billions.
Ant sociality, like that of the social wasps, bees, and termites, is expressed through a division of labor in which offspring that do not reproduce, called workers, assist their mother, called the queen, in caring for her brood, their future siblings. Despite the characterizations of Disney and Pixar, any ant recognized as an ant is female; males do exist, but they are socially useless and resemble wasps rather than ants.6 When I call an ant “she,” therefore, I’m simply reflecting reality. During their brief lives, males perform a single duty: they fly out of the nest, mate with a virgin queen (often several mate with one queen), then die. The queen will live much longer, starting her own nest and producing offspring for years from the sperm collected in this one mating flight. Because ant colonies are meant to be permanent, she and her workers, who live anywhere from a few weeks to a couple of years, will stay together. The only exception to this rule occurs when the workers rear the next generation of queens and males that depart their mother’s nest to produce the next generation of colonies. When a colony’s queen dies, with some exceptions we shall see later, the colony dies with her: her workers become lethargic and gradually expire.
In large part because colonies contain relatives, ants are altruistic, working without focusing on their own prospects for reproduction, which in any case are usually near zero. Edward O. Wilson and Bert Hölldobler further argue that colonies can be unified beyond familial bonds, as happens with humans. This allows for the success of colonies in which workers have multiple parents, including more than one queen.7 That’s not to say there can’t be discord in a colony. Among some ants, for example, workers, though unmated, can lay eggs that develop into males. Such workers form a pecking order in which those at the top forage less, receive more food, and are more likely to lay eggs.
Instead of maturing gradually, like a human, an ant hatches into a larva, the stage during which growth occurs; after a quiescent pupal stage, the adult ant emerges. A female ant’s size and accompanying functional role (or caste, such as queen, minor worker, or soldier) are largely determined by how much food she is fed as a larva, though temperature has an influence at times, and genetics can also nudge a growing individual toward a specific function.8 Queens and workers (and different workers in polymorphic species) are distinctive in appearance because body parts develop to different extents depending on the individual’s size. Adult ants do not grow, but workers tend to perform different tasks as they age. Young adults, identifiable by their paler color, remain in the nest and take on the lion’s share of the nursing responsibilities (in most polymorphic species these are handled by the minor workers), cleaning and feeding the larvae and, in species in which the larvae spin silk encasements before transforming into pupae, helping the adult ants emerge from their cocoons.9
In addition to being highly social, ants are global, native to every continent except Antarctica and residing in virtually every climate. They have achieved universality by conquering Earth’s most abundant habitat: the interstices of things, including the most secluded portions of the leaf litter as well as pores in soil, cracks in rock, and gaps and hollows in trees, right up to their crowns. As ants sweep through and conquer, they force other small animal species to the fringes of this prime real estate.10 Ants sprang to prominence at the end of the Mesozoic Era, as the dinosaurs neared the end of their reign and when flowering plants first exploded in number, providing generous and distinctive crannies suitable for ant foraging and habitation, not to mention tasty seeds, fruit, and other edible plant parts and the insect prey that feed upon them. Housed and fed for success, ants have reigned over the landscape ever since.11
Marauder ant major workers serve as heavy-duty road equipment. This one in Singapore is gnawing at a twig, which she later dragged off the trunk trail.
1 strength in numbers
We tracked marauder ant trails on steep forested slopes, accompanied by the “wish-wash” sounds of hornbills in flight and mournful calls from a green imperial pigeon. As nightfall approached, we made our way back to the village of Toro, in a valley of brilliant green paddy fields at the edge of the forest. My guide, Pak Alisi, invited me into his home for tea. “You know,” he said, “here we call the ant you study ‘onti koko.’ That means you always find many together.”
Yes, I agreed. With the marauder ant, the group is everything.
FIELD NOTES, SULAWESI, INDONESIA, 1984
“We have three kinds of ants here,” declared Mr. Beeramoidin, the forestry officer at the village of Sullia in India. “A black one, a big red one, and a small red one that bites.”
I was twenty-four, a graduate student on a quest for the ant I had reason to believe had one of the most complexly organized societies in existence. A column of dust-speckled sunlight emblazoned a rectangle on the floor too bright to look at directly—a reminder of the intense dry heat outside. It was late November, and I was worried my choice of season wasn’t giving me the best weather for ant hunting.
As Mr. Beeramoidin spoke, his round, bespectacled head rocked from side to side. I had learned that this meant his attention was friendly and focused on me, and though I had only been in India a month, I had already adopted the same habit. I also found myself chewing betel nut, wearing a Gandhi-style lungi around my waist and flip-flops known locally as chapels on my feet, and using words like lakh, meaning a hundred thousand, to describe the number of workers in an ant colony.
Rocking my head in turn, I told Mr. Beeramoidin it was likely that scores of distinctive ants lived within a stone’s throw of his office, though even an experienced person would need a strong magnifier to tell many of them apart. I sought just one of them, Pheidologeton diversus, a species to which I later gave the name “marauder ant.”
In 1903, Charles Thomas Bingham, an Irish military officer stationed in Burma, provided detailed and theatrical descriptions of this ant. In one memorable passage, he wrote that “one large nest . . . was formed under my house in Moulmein. From this our rooms were periodically invaded by swarms, and every scrap of food they could find, and every living or dead insect of other kinds, was cleared out.” The locals found the swarms overpowering. “When these ants take up their abode in any numbers near a village in the jungles, they become a terrible nuisance. . . . I knew of a Karen village that had absolutely to shift because of the ants. No one could enter any of the houses day or night, or even pass through the village, without being attacked by them.”1 In spite of the vividness of Captain Bingham’s report, the group remained a biological mystery.
I had arrived in India in the fall of 1981, primed to explore the social lives of the minor, media, and major workers of Pheidologeton diversus. My first stop had been Bangalore, more specifically its prestigious university, the Indian Institute of Science. My host was Raghavendra Gadagkar, a professor whose subject was the social behavior of wasps. He believed in learning from experience and smiled at my naïveté and youthful enthusiasm. Rather than teaching me how to eat rice without utensils, in the local fashion, for instance (the nuances of handling hot food bare-handed are many), he dropped me at the door of a local restaurant, recommended I order the “plate meal,” and came back for me an hour later. During that first lunch I spilled more than I ate.
Bangalore