The earthworm fauna of South Korea is dominated by the family Megascolecidae and identified 101 species, with 12 species in Lumbricidae, 9 species in Moniligasteridae and 80 species in Megascolecidae (Fig. 1) (Hong, 2000, 2005; Hong et al., 2001). In general, earthworms are classified into three types based upon life style and burrowing habit (Bouche, 1972). The epigeal forms (e. g., Lumbricus rubellus and Eisenia fetida) hardly burrow in soil at all, but inhabit decaying organic matters on the surface, including manure or compost heaps. The endogenous species (e. g., Allolobophora chlorotica and Allolobophora caliginosa) produce shallow branching burrows in the organo-mineral layers of the soil. Lastly, the anectic forms (e. g., L. terrestris and Allolobophora longa) are deep burrowing species, producing channels to a depth of one meter or more. Megascolecidae species identified in Korean ecosystem come under anectic forms. Occurrence of earthworms in agroecosystem appeared the most individuals of Amynthas agrestis, Amynthas heteropodus and Amynthas koreanus (Hong & Kim, 2007).

1.2 Biomonitor for biological hazard assessment on soil contamination

Concerns about contamination of soil and detrimental effects of contaminants on the living environment have resulted in a strong and growing interest in soil organisms among environmental scientists and legislators. Legislation in many countries has recently focused on the need of sensitive organisms from the soil environment for environmental monitoring. Many toxic materials have been accumulated along with food webs. The decomposer levels are frequently the first to be affected since the organic matter and the soil are the ultimate sink for most contaminants. Ecologically, earthworms are near the bottom of the terrestrial tropic levels. The effects of contaminants on earthworms which were kept in soil in the laboratory have been studied (Edwards & Thompson, 1973). These tests tended to produce consistent and reproducible results because 10 individuals of E. fetida were used and these worms were an intimate contact with pesticides. van Hook (1974) demonstrated that earthworms could serve as useful biological indicators of contamination because of the fairly consistent relationships between the concentrations of various contaminants and mortality of earthworm. The basic requirements of finding a species easy to rear and genetically homogeneous could be fulfilled by using representatives of the species, although there have been arguments for the use of Eisenia andrei or a genetically controlled single strain of the E. fetida complex (Bouche, 1992). Callahan et al. (1994) have suggested that E. fetida may be a representative of the species, Allolobophora tuberculata, Eudrilus eugeniae and Perionyx excavatus based upon the concentration-response relationship for 62 chemicals when applying the Weibull function. Habitational earthworms, including E. fetida, are useful as biological indicator species in the ecological sense or a more useful biomonitor species. It has been proposed that A. heteropodus could be adopted as a bioindicator in agroecosystem because of dominant species in South Korea (Kim et al., 2009).