A number of studies have been conducted on the standard worm Eisenia fetida/andrei. Some of the responses of earthworms to sublethal concentrations of pesticides is shown in Table 1. Zhou et al. [30] have reported that the weight of the earthworms was a more sensitive index compared to the mortality in indicating toxic effects of acetochlor and methamidophos. Espinoza-Navarro and Bustos-Obregón [31] treated Eisenia fetida with organophosphate insecticide malathion and Bustos-Obregón and Goicochea [3] explored the effect of exposure to commercial parathion on Eisenia fetida; both observed decrease in the body weight of treated worms. Weight loss has also been reported for organochlorine pesticides intoxication [18, 32, 33] and for the effects of fungicides and herbicides in Eisenia fetida and Lumbricus terrestris [34–36]. Choo and Baker [37] found endosulfan did significantly reduce the weight of juvenile Aporrectodea trapezoides within 5 weeks when applied to soil at normal application rate in both the field and laboratory while fenamiphos did so at normal application rate in the field only. Both fenamiphos and methiocarb reduced earthworm weight in the laboratory when applied at 10 normal rate. Weight loss appears to be a valuable indicator of physiological stress, related to the degree of intoxication and time of exposure [22, 38]. Coiling, another symptom seen in 100% of the Parathion treated worms, is related with weight loss and is regarded as the consequence of alteration in muscular function elicited by organophosphoric pesticides which may explain the difficulties for locomotion of the intoxicated worms and their relative inability to feed themselves [3].