Significance of the Western Harvester Ant in Bioturbation and Pedologic Development: Results of Neoichnology Laboratory Experiments.

Ants are often overlooked as a principle component of soil development, impart, because the general knowledge of their subsurface behaviors and construction methods is unknown. We present results of two neoichnological experiments where the burrowing behaviors, nest ontogeny, and sediment mixing patterns of the western harvester ant were observed and documented. The first experiment, designed as 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 for 6 weeks. The second experiment was constructed in a 112 x 54 cm glass enclosure, containing interbedded layers of natural sand, layers of sand colored yellow, red, and green, and layers of gravel colored pink, blue, and white composed of shells. One thousand ants were added to this set up and allowed to burrow for 12 weeks. Ants translocated sediments upward as well as downward from layers within the nest. Mixing took place within and between the different layers as well. When new material was added to the surface of each experiment, it was incorporated into the subsurface nest. Ants excavated and backfilled the nests by raking, pushing, forcing, pulling, and carrying sediment. Ants constructed galleries that averaged ~1.5 cm in diameter. Chambers varied from a few cms long and high to ~10 cm long and 2 cm high. Ants hung upside down and pulled material from the ceiling to enlarge the chambers, as other ants removed this material from the area. Excavated sediment was removed from all horizons and deposited at the surface as a large cone. Excavated material was used to reinforce walls or to backfill previously constructed galleries and chambers, as well as to build the surface mound. These behaviors and mixing patterns are important for understanding the influence of ants on bioturbation and soil pedologic development.