THE ROLE OF ANTS IN FORMING BIOMANTLES

Soil biomantles are notable components of many midlatitude, subtropical, and tropical soilscapes. The role of ants in producing them has historically elicited genetic interest, and some controversy. Interest began in 1881 with the appearance of Darwin’s book on soil formation by worm bioturbation, in which ants are mentioned. Subsequent attention to the theme involved leading scientists during the 19th-20th century transition period. More recently studies of archaeological site formation processes have noted the contribution of ants to the process of bioturbation in burying artifacts and mixing the remains of discrete cultural components. This paper reports on several post-Darwin highlights of ant bioturbation, the 'sinking' or burial of surface features on archaeological sites, and quantitative data for soil bioturbation volumes produced by Lasius neoniger and Tetramorium caespitum during one activity season in Champaign-Urbana, Illinois. Extrapolating these data with time suggests that the two species play key bioturbative roles in producing comparatively thin (~30-60 cm) sandy and or silty biomantles in the Upper Mississippi Valley region. Recent work by Donald and Diana Johnson in Texas and Louisiana suggests that Atta texana, the leaf-cutter (parasol) ant, a prodigious and legendary soil bioturbator and mound maker, plays a key and probably dominant role in producing comparatively much thicker (up to 2 m and greater) sandy biomantles found in the Gulf Coastal plain. Ant bioturbation is part of the development of even thicker biomantles in the tropics.