Specific gravity and dropping speed in eggs ofOncomelania hupensis, a snail intermediate host of Schistosomiasis

Oncomelania hupensis (Gredler, 1881) is an intermediate host of Schistosomiasis japonica in China. In order to understand the factors controlling sedimentation and drifting of adult snails and snail eggs in rivers, three aspects were investigated by experiment. Firstly, the specific gravity of the snail eggs was found to be 2.29 g/cm3; secondly, the range of dropping speed of the snail eggs through a water column was found to be 1.19 to 3.77 cm/s; thirdly, a formula for dropping speed of the eggs was established. The formula was statistically validated by comparison with observed values. The results are relevant to both the development and design of irrigation scheme, and also to river management, where dispersal of snails and their eggs needs to be controlled.