Distribution of Oncomelania hupensis in the Napu Valley of Central Sulawesi, Indonesia.

Fifteen colonies of Oncomelania hupensis were found near trails transecting the North Lore District, Napu Valley, Central Sulawesi. Habitats were in abandoned rice fields, uncultivated grazing areas for livestock, roadside ditches and, in one case, an actively worked rice field. Marsh grasses, Ischaemum barbatum and Laersia hexandra, were the most common plants in oncomelanid habitats. Other mollusks found in association with O. hupensis were Radix sp., Melanoides sp., Gyraulus sp., Idiopoma sp., Thiara sp., Opeas sp. and Indopyrgus sp. in that order of frequency. Schistosoma japonicum cercariae, as determined by mouse exposures, were shed from snails collected at four foci. In Sulawesi, O. hupensis and S. japonicum were found in high mountain valleys near, or above, 1,000 meters in elevation. Oncomelania hupensis, however, were not found in what appeared to be suitable habitats at lower elevations in the same drainage systems.