It is not unreasonable to think that something harmful to earthworms would also be detrimental to soil tilth and plant growth. However, a study done at an alpine meadow on the Tibetan plateau demonstrated a surprising indirect effect of the presence of predatory beetles. The beetles did not suppress earthworm density. Rather, earthworms increased their depth of habitation, improving deeper soil layers, which resulted in better plant growth and greater plant biomass.
Journal of Animal Ecology, 82 (4) pp 749-758