Mining For Sunlight

by Pavel Vakhlamov, University of New Mexico

The western harvester ant, as known by many hikers, outdoor enthusiasts, and admirers of the New Mexican landscapes, is an unexpected and daring territorial contestant and is widely recognized for its poor hospitality toward intruding giants (that would be humans). Although small in size (3/16” to 1/2" or 0.47cm to 1.27cm long) it is fairly large in comparison to many other ant species (See top left of image). The harvester ant serves no threat to its natural neighbors because its primary diet consists of plant seed harvest, from which it derives its common name. Its habitat spans across the entire state of New Mexico and sizable colonies can be easily spotted due to altered and eradicated vegetation surrounding it (See bottom left of image). It is not uncommon for such colonies to clear a circular pattern up to 7 meters (23ft.) in diameter and larger. In some places, such as the Sevilleta National Wildlife Refuge, massive colonies can be recognized on aerial photographs, undoubtedly illustrating significant impacts of the harvester ant activity on surrounding landscapes.

The complexity of colonial structures and the harvester ant’s ability to alter its surrounding environment is mind boggling (See top right of image). Many scientists agree that every alteration during construction of a nest serves vital purpose in the succession of the colony. By clearing surrounding vegetation, the newly constructed subterranean complex is able to receive heat from sunlight needed for larval incubation. Reducing density of the surrounding subsurface by removing smaller soil particles and covering the surface with small gravel, the harvester ant is able to achieve sufficient heat dissipation to the lower levels of the complex. In some areas of the Bandelier National Monument, near Los Alamos NM, these species have been documented to line the surface of their nest primarily with transparent volcanic glass mined from the volcanic tuff substrate (See bottom right of image). Some scientists speculate that by doing so, a lens effect is achieved, concentrating the incoming sunlight, allowing for deeper heat transfer.

On average a single colony can house between 9,000 and 10,000 sterile females, also known as workers, extend as deep as 3.7 meters (12 ft.) below the surface and reign for up to 12 to 15 years. During the lifetime of a colony, detrital and other unconsumed organic matter is stored in subterranean chambers, as well as on the surface along the circumference of a cleared plot. Such prolonged and dynamic activity results in substantial accumulation of nutrient deposits, which become available as a nourishing fertilizer for vegetation recovery once the colony is abandoned.

Although the harvester ant is a vegetarian, it is armed with powerful weapons on both business ends of its body. Powerful mandibles are able to remove large seeds from grass pods, but can deliver a powerful bite to any foe trespassing on its territory. In case that is not enough of a deterrent, a small stinger located on the tip of its abdomen can provide an injection of toxic venom, penetrating the intruder’s skin. Such defense mechanisms and teamwork coordinated by chemical signals released during confrontation will ward off any adversary. Several smaller ant species, recognizing the power of the harvester ant, seek protection from the big sister (all workers are sterile females) by building colonies on the outer edges of the nest’s clearing.

Photography acknowledgments: Bottom right: K. Ingham, Frijolito Ruins Loop hike in October 2003. Top right: C. F. Badland and courtesy of W. R. Tschinkel. Bottom left: W.P. Armstong, 2009. Top left: A. Wild.

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