Field and laboratory observations on terrestrial planarians from modified habitats in New Zealand

New Zealand agro-ecosystems are presumed to be exposed to more of the factors naturally controlling planarians than are those northern hemisphere habitats which have been colonised by austral planarians. Observations on planarians in pastures, maize fields and horticultural situations are described. Up to 1000 lumbricid earthworms m(-2) can be found in the same pasture as planarians; in such cases the native planarians are apparently preying on introduced European lumbricid earthworms. Work is required to determine whether such coexistence is due to natural factors regulating planarian populations in New Zealand, or to the dominance of endogeic lumbricids in New Zealand in contrast to the greater prevalence of anecic lumbricids in European agro-ecosystems. Although typically recorded under debris on the perimeter of agricultural fields, planarians do occur in midfield situations. Laboratory studies of predation are discussed. Under sheltered debris in modified habitats, some populations of terrestrial planarians appear stable from year to year; under more exposed debris and in open fields, there appears to be a strong seasonal pattern which may be controlled by soil moisture; there is some evidence that small planarians do arrive in mid-field situations but fail to establish viable populations. In this area, too, there is a need for biological information so as to understand better colonisation and invasion of other ecosystems by terrestrial planarians.