Two unmanaged sites (blackland prairie and deciduous woodland) in Walker County, southeastern Texas, were sampled monthly from February 2000 through January 2001 to determine effects of temperature and moisture on activity and population density of earthworms. The blackland-prairie grassland site supported an endemic earthworm fauna of two species of Diplocardia. A population of Diplocardia invecta was most numerous in the deep clay soil of this grassland site. The deciduous-woodland site supported a population of the exotic species Amynthas corticis (syn. Amynthas diffringens). This epigeic earthworm occurred in an isolated patch of disturbed, sedimentary clay soil in an otherwise sandy area. All observed D. invecta demonstrated seasonal vertical migration, but were quiescent from June to October. All observed A. corticis remained seasonally in the upper 10 cm of woodland soil, but were not observed during July, September, or October. Soil temperature and moisture at depths where earthworms occurred did not differ between the two sites from February through May and from November through January. Juvenile, adult, and total monthly population densities of both D. invecta and A. corticis varied due both to seasonal attrition and reproduction.