Adventures among Ants. Mark W. Moffett
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the other and wins.
THE NEST
Like most ant species, the marauder ant is a central-place forager, meaning its food supplies are funneled to a single central nest, which houses the queen and her brood. It is here that the society invests most heavily in defense, which makes excavating a marauder ant nest excruciating for scientist and insect alike.
But I had to do it. Studying marauder ants without looking in a nest would make as much sense as studying people without looking in a house. I also knew the ants well enough not to take my first attempt at snooping into their home lightly. Thinking the whole business out in advance, I selected my combat gear: long pants, a long-sleeved T-shirt, a pair of tightly woven socks, and tough boots. Arriving at the Singapore Botanic Gardens, I tucked the shirt into my pants and the pants into my socks and advanced toward the nest with a sharp-tipped shovel. Hovering over the nest, I breathed deeply for a moment before slamming the shovel into the earth. I had loosened a tiny chunk of nest soil; immediately a mass of enraged ants poured from the entrances. I threw the soil to the side and dug in again. And again. It took only a few tossed scoops before workers of all sizes had swarmed over my shoes and socks and up my pants and shirt to the first exposed skin they could reach: my neck and wrists.
When I could no longer tolerate the hundreds of bites, I ran to where I was out of range of the nest and scraped the ants off my skin and clothing. Then I grabbed the shovel anew and leapt back into the fray.
Repeating this cycle a few times, I found that the horde of minor workers pouring from the expanding gash in the soil had moved out many meters. Adding to the problem, the ants knocked off my body had spread out to the safe havens I’d used previously. Eventually, I had to sprint away from the nest to find a moment’s respite from the desperate defenders.
The thrill of a dig is in locating the queen. A marauder queen is a good runner, and during the time it takes to excavate a nest she’s likely to have been on the move, which makes it hard to know where she normally resides. On my first excavation, she was cloaked by an entourage of workers of all sizes and as a result—ouch!—a pain to catch.
It is yet another example of the value of media and major workers that battles between their colonies are fought only by the minor workers, while the larger ants—the heavy artillery—enter full combat mode only at the most desperate hour: when the nest is threatened. This distinction makes military sense. In 1914, the British engineer and military theorist Frederick Lanchester proved the advantage of outnumbering the enemy, even using troops of inferior quality, when battles are fought in large-scale formations. Hence, the minor workers, which per capita require little in the way of resources for a colony to rear and maintain, form a kind of “disposable caste” for both combat and predation. During colony conflicts, fights are one on one, making for a battle of attrition in which quantity trumps quality.10
After witnessing an excavation, Paddy Murphy claimed to be in awe of my tolerance for marauder bites. However, the payoff was a delight: I got an inside look at the marauder’s home life. Their nests are often at the base of a tree, where the colony takes over available hollows such as abandoned rodent burrows, cavities left when a root decays, or even buried jars—any space in the earth will do. Suspended among the heaps of workers in these hollows are eggs, larvae, pupae, and victuals such as seeds and legless animal bodies. Also present are smaller, outlying chambers dug by the ants themselves, an activity that results in telltale piles of soil around the tree base. These are near, but typically separate from, the ants’ midden piles of seed husks and discarded insect parts.
In the outlying chambers are the pale callows, adult ants so young their exoskeletons haven’t fully hardened. Here, the young minor workers take on the role of nurses, tending the brood. Also crammed in these chambers are major and media repletes—a special caste in the marauders, distinct from other medias and majors. With their bloated abdomens, repletes serve as living pantries, storing and then regurgitating liquid food to other colony members. (The food is oily, suggesting that repletes take their fill of oil-rich seeds.) Excavating my first nest, I saw the repletes much like fat cells in a human body and wondered how many a colony needed to stay healthy. The question still needs an answer. The repletes’ liquid stores are only a part of their hoarded reserves: workers also stockpile seeds and insect flesh from recent catches. Because repletes’ reserves do not spoil, it is possible they are drawn from mostly in exceptionally lean times.
It’s unclear how individuals are chosen to take on the indolent life of a replete, leaving others to toil outside, but their lifestyles couldn’t be more dissimilar. Repairing trails and mangling prey, “orthodox” medias and majors strut high on their legs. In the darkness of the nest, their replete sisters crawl with their bodies pressed to the ground or bury themselves among the brood, interlinked with the outstretched legs of resting minor workers.
Determining the population of a marauder nest—typically between 80,000 and 250,000 workers—can be an adventure. For an excavation in Thailand, for example, I traveled north of Bangkok to Tam Dao National Park in the company of primatologist Warren Brockelman, who was studying the brachiating ape known as the gibbon. At a station inside the park we heard stories of a local tiger that had grown so brazen that he would leap through open windows and drag out the bodies of his victims. Sleeping that first night in Warren’s open lean-to, I was awakened in the dark by the sound of rumbling breath. At sunrise Warren pointed to tiger prints in the dirt.
Later that morning I joined Warren to watch a pair of pileated gibbons sing a duet in a little valley. Noticing a marauder trunk trail nearby, almost invisible in the heavy leaf litter, I fell to my knees and for over an hour inched along the trail, grateful to forget all those vertebrates, whose simple behaviors, like leaping through windows, made the marauder ant’s superorganized throngs seem all the more awe inspiring, small or not. Oblivious to the time, I continued until I found myself near the crest of a hill. At the crest was the columnar trunk of a dipterocarp tree, and at the base of the tree, marked by the discarded soil and ant trash spilled around its buttressed roots, was the nest, at last! For several heedless seconds, I scrambled around the tree on my hands and knees, in the classic “compromising position.” Then something caused me to look up, and there, just two yards away from me, was a bull elephant. Wrinkled and gray, he stood absolutely still and silent, with his right forefoot lifted as if he’d been about to step forward. For that moment only his eyes moved, the eyelashes rising and falling in a blink. When he turned and crashed into the forest, all I could think of was how unfathomably larger than an elephant I must appear from an ant’s perspective.
After recovering from the unnerving but thrilling encounter, I exhumed the ant nest with a foldable camp shovel, put several kilograms of ants and soil in a plastic bag, and stumbled back to Warren’s jeep, a half-hour away. That evening at the park hostel’s dining room, I convinced the cook to let me put my bag of treasure in the kitchen freezer. I needed to freeze the ants—thus incapacitating or killing them—in order to separate them from the soil so I could make my counts. I went to bed satisfied by a good day’s work.
But the next day a different cook was on duty. No one had told him about my ants, and he’d removed the bag from the freezer and placed it on the floor. The ants had revived, cut their way through the plastic, and stormed the kitchen. I managed to round them up after an hour, enduring countless bites to my fingers. Grateful that my knowledge of Thai curses was meager, I also managed to mollify the new cook with two Singha beers and many compliments on his stir-fried pad see ew.
The painful bites and Thai curses were forgotten once I had tallied the data and gone to relax in the hostel’s dirt-floored canteen, where I ate sticky rice under a ten-watt bulb while trying to impress two girls, on holiday from Australia, with how cool it was to be an entomologist (and when that didn’t work, a National Geographic photographer). But I’d forgotten one of the most important lessons of marauder ant research: one worker always stays behind, after a skirmish, waiting for the proper moment to exact revenge. This time it happened midway through my meal. I started to howl and slap myself, and the girls disappeared.
BREAKING CAMP
Marauder ants are often on the move, and it is here that their roadways again play a role. I have come across dozens of migrations in which the whole society