Boundaries
by Jack Nisbet

Jack Nisbet is the author of The Mapmaker's Eye, Sources of the River, Purple Flat Top, Singing Grass, Burning Sage and Visible Bones. His newest, The Collector, is due out in October.

Carpenter Ants on the Wing and in the Wood
May 2007

When the British team of the Northwest Boundary Survey hired naturalist James Keast Lord in 1858, they assigned him to collect bird and animal specimens along the 49th parallel from the lower Fraser to the Continental Divide. Lord took to his duties with relish, sending home an impressive sampling of whatever living creatures came within range of his shotgun. He was at Fort Colvile in June of 1860, watching common nighthawks -- one of the last spring migrants to arrive in the north Columbia country -- swoop and boom through the dusk of sunny evenings. When Mr. Lord procured one of the birds (which he called goatsuckers) for his collection, he penetrated deeper into the food web of the North Columbia country that he could ever have imagined.

At Colvile in June 7 I observed a great number of these goat-suckers in company with the green-backed swallow, and what I imagined to be the black swift...I succeeded in getting three swallows and one goatsucker, a male, its stomach was gorged with winged ants -- a flight of these insects had, I imagined, attracted all these birds.



Dr. Laurel Hansen is a biology professor at Spokane Community College who specializes in ants. Her particular interest is carpenter ants, and J.K. Lord's record of an aerial display of ants in early June sounds to her like a nuptial flight. This raises all kinds of questions about what life might have been like at Fort Colvile 150 years ago, and how much the families stationed there might have shared with local residents today. Did lines of big black ants crawl through their kitchen? Were children kept awake by the sounds of strong jaws chewing through the night? Did winged ants skip across the floor during the first fair days of spring?

Carpenter ants belong the genus Camponotus, and more than half a dozen kinds might be found in the North Columbia country. The most noticeable, and the most studied, is Camponotus modoc. A mature colony of these carpenter ants can contain up to 100,000 workers, each produced by a single queen. Camponotus majors, the largest members of a colony's all-female work force, are the largest individual workers of any North American ant. As for longevity, Dr. Hansen observed one colony in the base of a dying tree for 21 consecutive years, until the tree blew down in a windstorm.

In order to feed these many thousands of workers that make up the colony, carpenter ants forage as predators, tap into plant sap, tend herds of aphid like farmers, and scavenge anything that dies nearby. Only a small percentage of the colony goes out after food at any one time, and over the course of a season their methods change dramatically depending on the needs of the colony, outside threats, weather conditions, and seasonal rounds. The diet of C. modoc includes grasshoppers, crickets, leafhoppers, aphids, crane flies, mosquitoes, honeybees, moisture ants, thatching ants, spiders, and the larvae of butterflies, flies, and bees. Some of their prey, such as forest tent caterpillars, douglas fir tussock moth pupa, and western spruce budworm pupa, are significant pests in our forests, and since carpenter ants are so abundant, the importance of their role in forest ecology cannot be ignored.

Around human dwellings carpenter ants will go after anything sweet, including pet food. If there is a queen beneath your house, winged carpenter ants will emerge in May and begin to beat against your windows. Known as alates, these winged ants are both males and females that have developed during the previous year and over-wintered deep inside the nest. When day length, temperature, and humidity send the right clues, all the alates gather at the nest entrance, "sunning" in the spring light and twisting their abdomens in an excited dance. They take off on their nuptial flight in dense clouds that can be mistaken for smoke wafting off treetops and provide food for any number of insect-hawking birds, including J.K. Lord's nighthawk. In the air, the males copulate with the females, who store the sperm in internal pockets. While the males soon die, surviving females spiral down to the ground to make their attempt at becoming full-fledged queens.

Upon returning to earth, each potential queen bites off her wings and begins to search for a suitable site at the base of a dying tree. She scrabbles down into the litter and lays between 4 and 25 eggs. Living off her resorbed wing muscles, she incubates the eggs, helps the white larvae to hatch, feeds them nectar from her abdomen, and nurses the grubs through four separate instars of growth. It takes three weeks or so for the young to finally emerge as her first brood of worker ants, very small female helpers called minors. But these minors can feed, and bring food back to the queen. They burrow further into the ground or excavate tunnels in the decaying wood, finding better protection for their mother. The cycle of the colony has begun.

The queen lays another batch of eggs in the fall, fertilizing them with her stored sperm. These larvae over-winter before emerging as more female workers. If no raccoon or skunk digs them out, if no storm uproots their tree, if no rival colony of ants attacks and kills the queen, the second year sees more slow growth and more minor workers busily tending the brood: moving them often, carefully regulating their temperature, and caring for the now-sedentary queen.

In the third season, larger workers called majors begin to develop from the pupa. Now the cycle kicks into a higher gear, with the queen producing more and more eggs during her two annual laying sessions. Groups of workers might ascend the tree or the studs in a house above the protected queen to form satellite colonies. As long as there is food and good protection for the queen and her brood, the colony can thrive.

Trunk lines to dependable food sources might be traveled for years, leaving distinct markings across the landscape. Tubular pathways are fashioned of sawdust between stacked boards and along sill plates, patio blocks, sidewalks, and driveways. Inside walls, insulation bats and electrical wires serve as superhighways.

Food foragers represent only a small fraction of the overall colony, and a lot of workers simply hang out in the nest during the day, apparently doing nothing. But as soon as something happens that requires attention -- the swift kick of a kid to the stump, for example -- they somehow know exactly how to respond in order to restore the rhythm of the colony. Modern ant researchers, instead of describing an all-powerful queen who directs the flow of her workers, visualize each individual ant as a neuron connected into a sensitive and adaptable brain.

As the carpenter ant colony expands, the workers continually excavate more wood, not for food, as termites do, but to make room for more brood. Their excavations allow fungi and other creatures to enter the decaying trees; thus Camponotus play a key role in the cycle of decay and growth through the entire forest. That role is visible from the outside of the tree as well, because carpenter ants make up about 97% of the diet of pileated woodpeckers.

Two centuries ago, when the Hudson Bay Company laid the sills for Fort Colvile in the dirt, or buried their stockade uprights in moist ground, they were inviting infestations of carpenter ants. Today, when we stack firewood close to the house, close off vents to crawl spaces in the winter, use railroad ties for landscaping, or spread moist Douglas fir mulch around shrubs near the house, we are inviting the ants to live with us, too. While Camponotus prefer moist wood that has some decay fungi, they will infest sound wood and have no trouble excavating fiberglass insulation, flakeboard, drywall, polystyrene, or urethane. J.K. Lord might not have understood the materials, but he surely would have been familiar with the result: carpenter ants form an essential and inescapable part of the Inland Northwest.

Illustration: A common nighthawk feeding on a swarm of carpenter ants courtesy Thomas Bewick and Dr. Laurel Hansen

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