1. The predation and ingestion rate of Thais haemastoma on oyster spat is sensitive to temperature and salinity. The effect of salinity on predation rate was different at 20° and 30° C.2. The temperature threshold for predation was between 10° and 12.5° C; drills were not observed to feed below 7.5‰.3. Drills exposed to diurnal tidal fluctuations of salinity, reflecting the estuarine environment, had predation rates significantly less than those at the optimal constant salinity (20‰) at 30° C, but were not significantly less at 20° C. The predation and ingestion rates in the fluctuating salinity cycles were not significantly different than rates for drills at the constant acclimation salinities of 10 and 30‰.4. Predation rates were not significantly affected by drill sex or weight and length. However, the experiments were designed to exclude size effects by selecting drills within a size range of 45 to 55 mm.5. Predation rates were not significantly different between large drills feeding as individuals (1...