An ant does not necessarily have an affinity for gold; to her it is just another fragment of earth to transport when constructing tunnels, chambers, paths, and nest cones. Gold is one of the heaviest elements, nearly twice the density of lead. Still, ants can lift or drag many times their weight and at today’s gold prices taking a nugget from her could pay for your lunch.
Gold-digging ants have persisted in the Western tradition since the 5th century B.C. writings of Herodotus, and later Pliny the Elder. In Herodotus’ The Histories, giant ants in the vicinity of modern Afghanistan were said to mine gold dust that people would collect from their mounds. Although Herodotus’ story is not entirely factual, ants are premier miners and to geologists “the world’s oldest prospecting tool.”
Soil covers most of Earth’s dry land, cloaking bedrock. Ants, hauling up subterranean material and gathering weathered bits of rock and minerals from their territory for deposit on the colony mound, can provide a window into the subsurface. Thanks to the ant’s undertakings, prospectors have discovered rich lodes of gold, copper, nickel, turquoise, diamonds, and many other minerals and gemstones.
Most ants do not build above-ground nests or true mounds that have living quarters, but some species of the New World harvester ants (e.g., Pogonomyrmex sp.) are a remarkable exception in the American West. Some harvester ant species will build conspicuous, pebbly mounds. These ants are known to forage items of uniform size from many yards away and place them on their nest cones to armor and acclimatize the nest—likely to protect the mound from wind and rain erosion and to increase solar heating and retain water vapor.
The conical mound of the western harvester ant (P. occidentalis) is typically about a few inches to more than a foot high, has an average volume of about a cubic foot, and can be 3 feet or more in diameter. The size of the pebbles used, consistent with their mandible spread, is about 0.1 to 0.2 inch (2–6 mm) and they may carry up to about half a carat items (0.0035 ounce).
The mound itself is typically oriented— the long or shallow slope faces southeast to capture the energy of the morning sun, and the mound entrance is on the southeast in more than four of five mounds in southern Utah. The nest cone exterior is built of prudently selected pebbles, but can include dirt pellets, shells, charcoal, dried bits of vegetation, human artifacts (especially near roads), and of course gemstones and precious metals when in proximity to these deposits.
Harvester nests have a circular zone free of vegetation ringing the mound, called an ant disk or yard, which can be small or more than 25 feet in diameter. Often radiating from the disk are some three to eight cleared trunk trails or the “ant highway system.” Visible on the landscape from high above, estimates from aerial photographs indicate these barren disks can occupy up to 2 percent of the total ground surface in semi-arid climates.