Do exotic earthworms invade New Zealand native forests?

New Zealand forest soils contain a rich diversity of native earthworm species, while our pasture soils are dominated by exotic earthworms which were unintentionally introduced in the 19th century. In North America, the invasion of exotic earthworms into what was previously earthworm free forest is causing considerable ecosystem changes. The aims of this study were to determine whether exotic earthworms were present in native forest remnants adjacent to pasture soils and determine the implications of this on the native earthworm populations. Four forest remnants and a reserve adjacent to agricultural pastures were sampled in the Waikato, New Zealand. Forest-pasture transects were sampled and analysed for earthworms. There existed a clear distinction in the species composition of the earthworm communities at our sites, with exotic earthworms almost exclusively in pasture soils and native earthworms in forest soils. The presence of exotic earthworms in the forest was rare, with no earthworms detected 3 m into the forest, and only a few being detected 9 m downslope into the forest. Our results suggest exotic earthworms found in the forest represent only sporadic migration of earthworms.