by Jack Nisbet
With the goal of learning a little about the thatched mounds I kept seeing in the woods, I gave Dr. Hansen a call. She invited me to visit her laboratory between classes and did not waste any time with chitchat when I arrived.
“Formicas,” she said in a friendly way as she shook my hand. “That’s what we call the thatching ants. And, no, I don’t really know anything about them.”
This was not the answer I had expected to hear. “Aren’t you the expert?” I asked.
“Some people think so, but it’s really all I can do to keep up with carpenter ants,” Hansen said, then added, “Lucky for us, I have a student who is behind in his work and looking for extra credit.” She stepped toward a standard-issue metal garbage can and motioned for me to pull up a chair alongside hers.
Just the previous week, she had noticed a thatching ant mound at the edge of campus that lay within the staked boundary of a proposed parking lot. Before the bulldozers arrived, Hansen had dispatched her student, Eduardo, armed with a shovel and a heavy plastic leaf bag, to the spot. Following instructions, he had dug as deep as he could—at least as far down as the mound was tall—and returned with a bag full of dirt and thatch, along with an untold number of angry red-and-black ants. That had happened a couple of mornings ago, and Eduardo was due back to inspect his labor any time now.
Dr. Hansen and I peered into the can. We sat quietly for a few minutes, watching an unsorted maze of ants scurry across the throbbing mass of duff. Several outliers had tackled the side of the can and were making their way to the top. Hansen grabbed a jar from a nearby countertop and redaubed the inside of the can’s upper rim with a slippery mixture of petroleum jelly and mineral oil so that none of the emerging prisoners could ascend the lip. “It’s true,” she said as she neatly pinched a single female worker between thumb and forefinger and inspected it with a hand lens she carried on a string around her neck. “I don’t even know what these things are.”
Formica is the largest genus of ants in North America, with well over one hundred named species. These are often lumped into seven rough groups, with rufa covering most of the red-and-black ones in the Inland Northwest. But major taxonomic revisions were under way. A British Columbia colleague of Hansen’s thought he had identified seventeen different kinds of thatching ants spread across the province. That sounded like a few too many to Hansen, and she had decided to call them all Formicas for now. I was agreeing that that was fine by me when Eduardo arrived and pulled another chair to the lip of the garbage can.
“Well,” said the professor to him. “Looks like you did all right here—a fair sampling of the colony, and it’s beginning to come back to life. But it’ll be a while before we find out whether you managed to capture a queen.”
The three of us sat around the barrel and watched the ant sisters scurry about, making order out of chaos. Hansen waited for a while before asking, “Does any of this make sense yet?”
Neither Eduardo nor I had an answer for that, and neither of us budged until Hansen leaned forward to focus on something that looked like a tamarack needle, bobbing above the crowd. A female worker carried it with one foreleg stretched straight out in front of her and the other raised at a forty-five-degree angle, so that as the ant marched resolutely across the pile, the needle flowed forward like a war banner. Eduardo followed the ant’s actions carefully before finally nodding his head.
Nuptials
During several succeeding visits, my lessons took place against a similar backdrop of complex social activity. An intern would be tidying up with one eye on a tank of newly hatched walking sticks. One student would be laying out papers across a lab table; another would wander in to try to cut some kind of late-work deal similar to Eduardo’s garbage can project. Various faculty members dropped by with news, and once a custodian knocked politely to explain how he had handled the recent escape of a Madagascar hissing cockroach. My contribution was to collect any references to ants that I ran across in early fur trade journals or tribal stories and present them for Dr. Hansen’s consideration.
In April 1806, for example, as the Corps of Discovery paused at the edge of the Columbia River Gorge, Lieutenant William Clark welcomed spring activities there. “The air temperate,” he wrote. “Birds singing, the pizmire, flies, beetles, in motion.” Could the word “pizmire,” I wondered, offer a clue to our slang term “pissant”?
“Maybe,” said Hansen, politely making it clear that she had seen the quote before. She said that to most people, a “pismire” means any large ant belonging to the group that, like both carpenter and thatching ants, sprays threatening invaders with formic acid. She thought it was a Scandinavian term, but she heard it all the time in reference to the big black carpenter ant, Camponotus modoc. She was not entirely convinced “pissant” grew out of “pismire,” but she guessed it did make a little sense. “They live in a chemical world, after all. We’re so dull we think most things smell the same.”
Other mammals can receive such chemical messages more clearly. Across the Columbia Basin, tribal people utilized convenient depressions in open talus slopes as storage pits for roots, berries, and meat. I had heard that they would sometimes line such pits with duff from an abandoned thatching ant mound, because the scent of formic acid repelled any chipmunks or coyotes that might have designs on the food. Dr. Hansen was not surprised. “Not many animals want to mess around with ants,” she said.
Sometimes people did, even if it was by mistake. In early summer of 1858, John Keast Lord, a naturalist for the British team of the Northwest Boundary Survey, was plying his trade at Kettle Falls on the Columbia River. Over the course of a long evening he watched swallows, swifts, and common nighthawks swoop and boom above the river. As was his habit, Lord shot down one of the nighthawks and upon dissecting it discovered that “its stomach was gorged with winged ants—a flight of these insects had, I imagined, attracted all these birds.”
J. K. Lord’s tale struck a chord with Laurel Hansen, because it sounded to her as if the nighthawks might have been feeding on a nuptial swarm of carpenter ants—a key moment in the annual cycle she had traced for her doctorate. During one frantic period of her studies, Hansen had duct-taped many yards of mesh into a cocoon that enclosed her entire lab. When winged male and female breeders, called “alates,” emerged from a carpenter ant colony she had kept all winter, she watched them crawl up onto the highest desks and chairs in the lab and make the characteristic twisting twitches of their abdomens that meant they were ready to swarm. As the alates began to fly, she chased them around, trying to record the first detailed scientific observations of Camponotus modoc mating behavior.
“One thing about Mr. Lord,” she observed. “His June date seems a little late compared to the carpenter ant flights I’ve seen in my time. Could something have happened that changed their timing since the 1850s? I mean, that isn’t even yesterday for them.”
The alates in that nighthawk stomach launched Hansen into the concept of “Ant Time.” According to very clear amber fossils, ants diverged from a common wasp family relative almost a hundred million years ago, during the middle Cretaceous period. By the early Eocene epoch, fifty million years later, their social kin already dominated the insect world. Today there are species of bulldog ants in Australia that don’t appear all that different from fossilized Eocene individuals. Such deep-time connections make it difficult to grasp the time scale that ants inhabit, which is much more geologic than human, or to separate the threads of any particular type’s life history. For instance, Hansen had identified both pavement ants and pharaoh ants wandering around her campus. Both are cosmopolitan species, but up to now no expert has managed to pinpoint either kind’s exact place of origin.
“Think about it,” suggested Hansen. “How did they get here?”
It was easy to visualize some invasive species riding up from South America in the last century, hidden on a banana boat. Another queen might have ridden a storm system east from the Philippines a thousand years ago, or cross
ed from Asia to North America via Beringia in people’s belongings ten thousand years before that. But bulldog ant queens might have ridden separate tectonic plates while our present major continents slowly rotated away from Gondwanaland, tens of millions of years back.
A Practical Lab
During my ensuing visits, Dr. Hansen showed me an array of carpenter ants that she kept among the assorted live study insects that occupied a narrow alcove beside her laboratory. The ants never wandered far from a supply of decomposing wood that provided their shelter and food, and she could use them to illustrate various points to her students. Early on, she handed her magnifying loupe to me so that I could get a sense of how efficient a carpenter ant’s stout plier-like mandibles are for excavating old firewood from the inside. Then we moved back to the garbage can to contrast those pliers with the needle-thin pincers of Eduardo’s thatching ants, designed for carrying things or spearing larval prey. “You can tell the different shape by the feel of each one’s bite,” she assured me. In another of her cabinets, we looked at drawer after drawer of wood samples that carpenter ants had chewed and polished neatly along each tree’s growth rings. Most of the samples came from infested houses that Hansen had visited, but on a deeper level, the sister ants had excavated those galleries and chambers as they carried out their appointed work of composting Earth’s decaying biomass.
Carpenter ants and their relatives are so common in Northwest forests that large predators such as pileated woodpeckers rely on them for a sizeable portion of their diet. Thus it stands to reason that as long as people insist on putting up framed lumber homes in wooded habitats, the ants are going to pose an economic problem. Research has proved that in northern latitudes, carpenter ants inflict more structural damage than termites—a statistic that touches the reason why Dr. Hansen was originally drawn into studying these ants.
“Growing up on a farm, I was always interested in the social insects,” she explained. “When I told my advisor I wanted to investigate termites, he said, ‘Everybody looks at the structurally invasive termite mounds in the southeast. But nobody knows anything about the ants that are all around us right here. Especially carpenter ants.’ ”
That set her on track, and carpenter ants proved to be a good subject, because the Camponotus genus contains a reasonable number of well-defined species. In most of them, the many thousands of female workers, plus a few males for breeding, are born into single-queen colonies and remain extremely nest-faithful—any outsider that wanders in is immediately killed. Carpenter ants are polymorphic, meaning that the sisters grow into a range of sizes; this allows them to successfully tackle jobs of varying scale. They are a dominant species, with enough large workers to overwhelm most other kinds of ants when their territories conflict. And they are wonderfully adaptable even as they pursue their single-minded ways: female scouts exploring random paths through forest duff can switch immediately to the straight line of a foundation sill board or aerial telephone line if it leads to accessible wood on the other end. During the course of her studies, Hansen learned to take real satisfaction from the ants. She observed one Camponotus modoc colony that thrived for twenty-one years tucked deep into the base of tree on a bank over a pond until a storm toppled the entire nest into the water. A single queen, after one night of fertilization inside a nuptial swarm, had supplied that nest with regular new eggs for more than two decades.
Once Hansen understood carpenter ant life history, people began to ask her for advice about how to get rid of them. When she realized that she had a knack for putting that knowledge to use, she decided that a practical job—like visiting some horrified family’s alate-strewn bedroom and offering steps to remedy the situation—suited her better than abstract research. “We call it ‘applied science,’ ” she said.
Although Dr. Hansen had harsh words for pesticide companies that favored poisons over accurate data, she sometimes ran lab trials for businesses that had a more enlightened view of their work. She was always in demand—there weren’t that many people around who knew how to wrangle ants—and as someone who tried to solve most problems by convincing the ants to go somewhere else, she was particularly interested in fresh concepts.
On occasion, however, she could also be talked into more traditional experiments. Once I entered the lab to find every inch of table space covered with clear plastic sandwich boxes. An assistant had carved perfect circles from the lids of the containers before smearing their tops with a Teflon component to halt potential escapees. Hansen had loaded each one with the proper amount and strain of poisonous test bait, then somehow coaxed an approximately correct number of tiny sugar ants inside.
While the professor made her daily rounds with a clipboard, counting dead ants and making sure all else was in order, we caught up on various threads of news. Hansen had recently traveled to Southeast Asia for a conference, where she had mingled with peers from all over the world while visiting some astonishing ants in both city and forest. Back home, she had run a couple of workshops for professional pest control workers—“nozzle jockeys,” as she liked to call them, because until they met her, most thought their job began and ended with a backpack spray tank. “I can call them that,” she said, “because I listen to them and we can joke around. We’re trying to accomplish the same thing after all, and it’s a lot easier if you know what you’re doing.
“All this business”—she waved at the plastic boxes—“we have to think about it because ants are so intertwined with people. How many ants can you tolerate, that’s what it comes down to. Everyone seems to have a different threshold.”
I confessed that I had never lived in a house where a few winged carpenter ants didn’t appear inside the kitchen each spring. Unless their numbers grew into the hundreds, we managed to coexist. Hansen nodded. “Yet for some people, and for some businesses,” she said, “one single ant turns out to be too many.”
The Box
Dr. Hansen’s particular knowledge has gained her many friends, and one of them built her a glass ant farm about three feet square and the thickness of a small bookshelf. It came complete with a screened lid and a cleverly rigged water system that dripped through bottle caps mounted beneath the cover. Early one fall, Hansen had a couple of her students load the box with an orphaned mound of thatching ants, then heft it onto an open countertop in her lab. Because she wanted to put the colony to sleep for the winter, Hansen asked them to push the box flush against the wall and to cover the exposed side with heavy black construction paper. When I swung by one November afternoon, she stripped the paper off so we could have a look.
The ants had not spent all their time sleeping. From our side of the glass, we could see that they had layered the duff into a marvelous tunnel system, irregular but highly organized, like a crazily warped geologic syncline. In places where the tunnels occasionally swelled into larger chambers, Hansen tapped her forefinger against the glass. “Haven’t found any eggs or pupa yet,” she said. “Don’t know if there’s a queen or two hiding in there somewhere. But we’ll see once they really get going in the spring.”
Thatching ants are very different from carpenter ants, in that the female workers tolerate multiple queens in the same colony—what Hansen called “polygyny.” That means that new colonies can bud off an original nest into a scatter of smaller mounds. If a worker from the farthest related mound wanders back to the original colony, the sisters there allow her to enter unmolested. Such behavior runs utterly counter to that of single-queen Camponotus species, whose workers immediately attack any outside intruder, for territorial protection. Since polygynous ants have the potential for rapid expansion, troublesome invasive species always belong in this category. South American fire ants, whose red mounds dot fields across the southeastern United States, and Argentine ants, which apparently arrived in New Orleans in coffee sacks a century ago, have both spread across entire states like a slow-moving ground fire, and rank high in any local manual of insect problems. Native thatching ants, whose distribution circle
s the entire Northern Hemisphere, tend to remain more in balance with the habitats around them. They rarely get more than a passing nod from the pest control business.
“Balance,” said Hansen, “might not be exactly the right word.”
She told me about an extended colony of Formica rufa thatching ants in the Blue Mountains of northeastern Oregon. Researchers termed it a “supercolony” and had found reports of similar occurrences from Europe and Japan. The cluster of mounds, bounded by an abandoned sawmill and a commercial hot springs, covered ten acres of mixed coniferous forest. Several timber tracts around it had been logged to harvest trees damaged during a recent destructive outbreak of the western spruce budworm.
To test whether all of the individual anthills in the area had split off from one original queen, the researchers took workers from random mounds and reintroduced them across the colony. All were readily accepted by their sisters. But worker ants collected from mounds outside the area were immediately pinioned to the ground, then bitten and sprayed with concentrated formic acid.
The biologists mapped the breadth of the supercolony, counting more than two hundred fifty mounds randomly scattered throughout the acreage. Just over two hundred of those mounds were currently active, and the separate colonies varied widely in size. A formula was devised to calculate the volume of individual mounds above- and belowground, with the seven largest hills estimated to harbor more than one million ants each. As the total population approached sixty million individuals, the researchers realized that the food required by that number of ants would total close to a thousand pounds a year.
Thatching ants consume a host of different foods, depending on need and availability. Some colonies maintain large aphid herds, both to harvest the honeydew processed by these tiny suckers of plant juice and to eat individual aphids directly. But the épée-shaped mandibles of Formica rufa ants are perhaps best suited for skewering caterpillars and other insect larvae—say, for example, developing spruce budworms.