In its native region of the South Island, the flatworm is largely confined to sheltered areas on wet soils and is rarely found in farmland. Indigenous New Zealand earthworms are similarly limited in their distribution and this may partially explain why the flatworm is not noted as a problem in New Zealand.
The flatworm is harder to find in New Zealand than it is in colonised areas of the British Isles. This could be due to natural enemies attacking it (which we lack) or shortage of food. New Zealand earthworms may also have evolved defensive mechanisms to the flatworm. Our own earthworms lack these and this makes them particularly vulnerable to predation by flatworms.
Our studies in Northern Ireland have shown that the flatworm can disrupt earthworm communities and cause localised extinction of some species. This will inevitably have an impact on habitats in which this invader is found.
Yours faithfully, Rod Blackshaw Department of Agriculture for Northern Ireland Agriculture and Food Science Centre Belfast 17 January