H. assimilis decreased to near zero over time, for both control and Cu-contaminated soil in all temperature conditions. While H. assimilis decreased rapidly, H. aculeifer was increasing, which could indicate predation. Cortet et al. (2003) tested SMSs with and with-out H. aculeifer, and found that with H. aculeifer it was totally extinct after 30 days while without H. aculeifer the population of H. assimilis showed a slow decrease over time. The fact that other potential prey species of H. aculeifer (F. candida, E. crypticus) did not decrease could be due to higher reproduction rates (e.g. (Amorim et al., 2005) for F. candida) masking the predation effect. P. minuta possibly has a lower reproduction rate than F. candida (Dodd and Addison, 2010), which may explain for its population decline.