Abstract 1. 1. Water contents, desiccation rates and desiccation tolerances were obtained for five species of spiders from different habitats: Achaearanea tepidariorum, dry terrestrial; Dolomedes scriptus, semiaquatic; Oxyopes salticus, herb-layer; Pardosa lapidicina, ground-layer; Trochosa pratensis, ground-layer. 2. 2. Interspecific differences were found in water content. No trend corre-lated with habitat was evident. 3. 3. Log regressions of rate of water loss on weight for all species indicate that the dehydration rate in part is a function of size. 4. 4. Mean rates of water loss for species of similar size seem to be adapted to the species apparent habits and habitats. 5. 5. Body size and desiccation rate do not influence critical activity point (CAP) values; they may be genetically controlled. 6. 6. CAP values of A. tepidarirum and D. scriptus correlate well with the moisture characteristics of their habitats.