A CAST OF THOUSANDS: PRELIMINARY ANALYSIS OF A WESTERN HARVESTER ANT NEST CAST IN ALUMINUM FROM WESTERN KANSAS AND COMPARISONS WITH ICHNOFOSSILS OF PURPORTED FORMICIDAE CONSTRUCTION

Recently described ant-nest ichnofossils from the Neogene Ogallala Formation were identified through comparisons to casts of modern ant nests (Hymenoptera: Formicidae). To expand the database of known modern ant-nest architectures, we collected a cast of a western harvester ant (Pogonomyrmex occidentalis) nest during a field trial in Ellis County, Kansas. The nest was cast with molten aluminum, a method pioneered by ant researcher Walter Tschinkel. The method was modified with technology from the Fort Hays State Department of Art and Design. During the field trial, aluminum was melted with a mobile foundry and poured into the entrance of the surface mound of a western harvester ant nest. Pouring ceased when the metal began pooling on the surface of the mound. Following cooling, the nest was excavated and the 31 cm deep cast was cleaned. The upper ~10 cm of the cast contains superficial chambers, i.e., dense, complex, interconnecting and looped passages created mostly by enlargement of horizontal shafts. Superficial chambers represent the entire height of the nest mound and have a dimpled texture caused by the coarse grains used to construct the mound. Below the superficial chambers, chambers are more distinct, have smoother walls, and are more widely distributed both horizontally and vertically. These are connected by short subvertical ribbon-shaped shafts typically only a few cm in length. Two to three distinct vertical shafts are present, each containing horizontal chambers that increase in vertical spacing with depth. The longest of these cylindrical shafts is ~20 cm long, but the shaft likely penetrated deeper in the ground and was not cast because the aluminum cooled and created a blockage. Of the fossil nests (domichnia) interpreted to have been constructed by ancient ant colonies, the aluminum cast from western Kansas is most similar to those in the Daimoniobarax ichnogenus.