The water permeability rate of the shell wall of Bulinus tropicus (Krauss) was determined with tritiated water to be 1.74 ±1.06 μl water per 24 h. The osmotic pressure of the haemolymph increased three-fold to 300 ± 16 mOsm l−1 after 60 days at 85% r.h. of the air. The [Na] of the snail tissues increased from 38 ± 9.0 mMol l−1 to 68 ± 11.0 mMol l−1 after 60 days at 85% r.h., but at 96% r.h. the increase changed from 40 ± 7.0 mMol l−1 to 55 ± 6.5 mMol l−1. The [K] of the snail tissues increased from 30 ±10.1 mMol l−1 to 58 ± 11.2 mMol l−1 after 60 days at 85% r.h., but at 96% r.h. the increase changed from 30 ± mMol l−1 to 42 ± 10.2 mMol l−1. The oxygen consumption rate (VO2) decreased by 66% from 60.0 ±19.1μl O2. g−1 snail. h−1 to 20.5 ± 16.0 μl O2. g−1 snail. h−1 after 60 days at 96% and 85% r.h. In laboratory experiments without sunlight, snails were still alive after 5 months on mud. In field experiments conducted in direct sunlight on mud, snails were dead within 24 h. At r.h. of 96%, 92%, 85%, 74%, a...