Culture of commercially obtained Lumbricus terrestris L.: Implications for sub-lethal ecotoxicological testing

The use of commercially purchased or field-collected earthworms of unknown age, exposure or pre-treatment in sub-lethal ecotoxicological studies is questionable. In this study, adult (clitellate) Lumbricus terrestris, obtained from 5 commercial suppliers in the UK and also field collected, were kept under controlled environmental conditions (15 °C and 24 h darkness) in a sterilised loam soil and fed horse manure. Survival, biomass and cocoon production was monitored every 4 weeks over 1 y. Marked differences were recorded in survival rates (ranging from 40-100% after 40 weeks) and cocoon production (ranging from 15.1 to 32.2 worm⁻¹ y⁻¹) between treatments. Biomass in all treatments (mean mass 4.32-5.61 g at the outset) increased with time to week 20 (maximum 6.7 g) and then declined steadily (3.23-4.7 g at week 52). This pattern was also observed in cocoon production and was considered to be a function of an initial period of acclimation (0-12 weeks) followed by a period of high production (12-36 weeks) under optimal conditions and then fatigue (36-52 weeks) caused by reproductive exhaustion. Results suggest that earthworm origin may influence the validity and reproducibility of sub-lethal ecotoxicological studies and where applicable laboratory-reared earthworms of known age and history are recommended as test subjects.