Earthworms are usually considered beneficent soil engineers. However research in the Great Lakes Region of the USA has demonstrated that exotic invasive species of earthworms have altered hardwood forest ecosystems. Amynthas diffringens (Baird 1869), an exotic invasive earthworm from Southeast Asia, is in high numerical densities in hardwood bottomland forests soils of the Stephen F. Austin Experimental Forest of Nacogdoches County, Texas. Also present in these same soils are four native earthworm species, all which have a markedly different behavior from A. diffringens. A microcosm study examined the influence of A. diffringens on the incorporation of the O horizon, the formation of water stable aggregates, and changes in water infiltration in comparison to native earthworm species.