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  D e s e r t   E x p o s u r e   February 2012

Southwest Wildlife

Collective Wisdom

Individually, harvester ants don't look like much. But when they get together…

by Jay W. Sharp

 

 

Strangely, ants in general, and harvester ants in particular — seemingly small and humble creatures that live in dark chambers beneath the floors of our deserts — have long stirred the human imagination.

ants
.Harvester ant mound surrounded by cleared surface in the western flanks of the Organ Mountains. (Photos by Jay W. Sharp)

For instance, in the mythology of the Pimas — a tribe of the northern Sonoran Desert and probable descendants of the Hohokam Puebloan tradition — a solid sphere of ants served as the raw material from which the Creator made the entire earth, according to Natalie Curtis in her The Indians' Book.

In the folklore of the Isleta Puebloans — a community of the northernmost Chihuahuan Desert and cultural descendants of the Anasazi Puebloan tradition — Big Red Ants and Little Black Ants rescued Corn-stalk Young Man from a bewitched tree so that he could save his starving village from a crippling drought, according Charles F. Lummis in his Pueblo Indian Folk-Stories.

In the practices of the Navajos — pastoralists and gardeners of the Four Corners region and linguistic descendants of American Northwest Indian peoples — the harvester ants, or "big pinching ants," had to be placated by elaborate ritual if someone dared to disturb their mound, according to Stephen Welton Taber in The World of the Harvester Ants.

In a large body of work by modern scientists — very bright people who try to understand our world — harvester ants have become something of a legend because they raise baffling questions that almost seem to extend into the realm of mysticism.


Societal Riddles

 

In a way that mystifies the human mind, which has the inclination to institute leadership, delegate responsibilities, organize resources and set schedules to carry out tasks, a colony of harvester ants (like colonies of other ant species) operates perfectly well in the absence of any apparent central control or organizing force, according to Deborah Gordon, author of Ants at Work. A queen mother, who serves as a well-maintained egg-laying machine rather than a royal sovereign, founds a colony of harvester ants, which may grow to 10,000 to 20,000 individuals. With no evident guiding hand, worker ants — all female children of the queen — go about the complex business of tending their mother, protecting her eggs, nurturing their baby sisters, pampering reproductive sisters and brothers, excavating and maintaining labyrinthine chambers, harvesting and storing food seeds, grooming themselves and defending their colony.

In another unexplained phenomenon, all neighboring harvester ant colonies of the same species — with no obvious prior communications, coordination or cue among them — emerge from their burrows on a single climactic spring or summer day each year. They send swarms of young winged would-be queens with their winged male consorts swarming into the desert air, on missions to breed and establish new homes. In some puzzling way, all the colonies know the appointed moment. Most, including all the males, soon die because of exposure to the desert environment, starvation outside the nurturing colony or predation by various gluttonous ant lovers. A few lucky females, however, probably less than one percent, will manage to find new homes and establish new colonies, beginning with tiny burrows they excavate into the soil. The new queen carries within her the sperm from several different males.


The Ant

 

Hopefully, a harvester ant, which may belong to any of several black to reddish-brown harvester ant species in the Southwest, will not introduce itself to you with its extraordinarily painful sting. Especially among sensitive victims, it can induce a long list of discomforts, including extended pain, burning, hives, swelling, wheezing, sweating, faintness, nausea and piloerection (hair standing on end), according to Taber.

The sting may make you mad, too.

Closely related to the wasp and the bee, according to Floyd Werner and Carl Olson in Insects of the Southwest, the typical harvester ant measures about three-eighths of an inch in length. It has "a basket of long setae [stiff hairlike structures] on the underside of the head" that it uses to carry soil when excavating and cleaning its nest.

A colony signals its presence by clearing all vegetation surrounding the entrance to its nest, leaving a barren flat or mounded area — a midden — several feet in diameter. Earning the name "harvester ants," foragers collect seeds, especially from desert grasses, which they stash in underground storerooms. They may also prey on insects, especially termites, if they can find and catch them. They forego water altogether, depending on humidity within their nest for moisture.


The Colony

 

A colony begins fortuitously when one of the few winged and fully mated females, or queens, to survive an annual flight manages to establish a small burrow, most likely in an open area. The first thing any new queen ant does, according to William Atherton DuPuy in Our Insect Friends and Foes, "is to tear off her wings, which she never expects to use again now that she had made her marriage flight." After digging the burrow several inches in depth, expert Deborah Gordon writes, the new queen lays several eggs, her very first, which "become tiny, wormlike larvae, and finally turn into pupae, resembling ants enclosed in a papery case.… When an ant emerges from the pupal case [after several weeks] it is an adult and does not grow any more." The queen, who will now spend the rest of her life in total darkness, nurtures her first young, all female ants, very carefully, from her own fat reserves. She may even lick them like a mother cat licks her kittens.

ants
Harvester ants at nest entrance, desert floor,
southwestern New Mexico.

With an apparent inborn understanding of their respective roles, these ants — much smaller, for some reason, than their successors will be — set up housekeeping. They forage for seeds. They care for the next generation, working to make the fledgling colony viable before closing down for the coming fall and winter.

With the arrival of spring, when the ant community reawakens, the population divides into two groups, according to Gordon. About three-quarters of the ants — all females — will operate primarily in the depths of the nest. Some of these ants care for the queen, the sole, vital source of eggs for the colony. Some nurture new larvae. Others excavate new chambers to accommodate their growing numbers. Others store food in designated spaces. Still others maintain the nest, carrying ant trash and excavated dirt to the surface. Some, apparently, just hang around in case they might be needed.

The remaining quarter of the population — again, all females — stays near the surface of the nest. Again, by some unknown understanding, maintenance workers tidy up immediately around the entrance. Patrolling ants inspect the nest midden area, stop and interrogate intruding ants, and set the day's foraging courses. The foraging ants typically travel as much as 30 to 40 feet from the nest in their quest for food, collecting the seeds from perhaps dozens of nearby plant species. Meanwhile, still other maintenance workers police the midden surrounding the nest entrance. It appears, says Gordon, that the younger ants perform the subsurface chores, the senior ants, the surface duties. As ants age, they graduate from subsurface to surface duties.

 
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