Slopefield Allotments New Zealand flatworm report by Annie Robinson from Aberdeen University
New Zealand Flatworms
New Zealand flatworms exclusively feed on earthworms which are essential for maintaining good soil quality and the food chain. The flatworms are between 50 - 150mm long, flat with a dark brown topside and a creamy pale underside and edge, and are often found curled up like Swiss rolls. They are pointed at either end and covered in sticky mucus, trails of which are left wherever they have been.
The flatworm originated in the South Island of New Zealand where it is found in cool damp areas such as woodlands and gardens. The first confirmed record for this species in Scotland was recorded in 1965 in the Royal Botanic Gardens in Edinburgh and probably originated from infected soil imported with plants.
The flatworm has spread by local dispersal but originally into new areas by plant containers. This is borne out by it's
distribution, which centres around gardens and nurseries and is now found extensively throughout Scotland.
The flatworm starts life in an egg cocoon laid in the soil. The cocoon is about 5mm long and it is bright red when newly laid but rapidly darkens to black. Up to ten young hatch from each cocoon and are about 30mm long and creamy pink in colour. The flatworms are able to reproduce when they have grown to about 50mm but will continue to grow beyond this length.
Terrestrial flatworms are prone to desiccation so they are restricted to damp habitats. During dry spells they migrate downwards through the soil and aestivate in mucus lined cells until the weather becomes wetter again. They are most active at night and avoid light, hiding under objects on the soil surface or in the soil itself. The New Zealand flatworm dies quite rapidly at temperatures higher than 20C and is susceptible to freezing.
The flatworm feeds by wrapping its body around it's prey (earthworms) and secreting digestive juices onto it. The liquefied prey is then ingested through the mouth tube. Part of the large impact of the flatworm on earthworm population may be that the flat worm can follow their prey through their burrows within the soil.