SIGNIFICANCE OF THE WESTERN HARVESTER ANT IN SOIL BIOTURBATION AND PEDOLOGIC DEVELOPMENT: RESULTS OF NEOICHNOLOGY LABORATORY EXPERIMENTS

The influence of ants is often overlooked as a principle component of soil formation, impart, because the general knowledge of subsurface ant behaviors and construction methods is unknown. This paper presents the results of two neoichonolgy experiments using the western harvester ant Pogonomyrmex occidentalis to observe and document burrowing behaviors, nest ontogeny, and sediment mixing patterns. The first experiment, designed to emulate a hypothetical A-C-Ab-Cb soil profile, was constructed in a 32 x 32 cm glass enclosure. Fifty ants were added and allowed to burrow uninterrupted for 6 weeks. An intricate nest was constructed that comprised numerous interconnected galleries and chambers. Excavation behaviors observed included raking, pushing, forcing, pulling, and carrying. The second experiment was constructed in a 100 x 54 cm glass enclosure, containing interbedded natural sand, colored sand, natural sand, and gravel horizons. One thousand ants were added and allowed to burrow uninterrupted for 12 weeks. A similar intricate nest was constructed and the same burrowing behaviors were observed. A variety of sediments from all horizons were mixed by the end of the experiments. Sediment mixing included the upward displacement of sediments from all horizons, the distribution of sediments throughout the nest, and the downward movement of sediments from all horizons. It is evident from these experiments that ants play an extremely important role in pedogenesis not only by mixing sediments, but by mixing soil nutrients and organic matter as well.