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This study was carried out at Moor House National Nature Reserve, Westmorland, U.K. (alt. 549 m; 1800 ft), to test the hypothesis that superficial drying of the soil causes enchytraeid worms to move downwards. A significant correlation was established between low values of the Index of Humidity (I.H.) and low relative frequencies of worms in the surface layers of peat soils. No such correlation was observed in mineral soils. In samples taken at 4-hourly intervals in summer 1967, a fall of I.H. values from 6.5 to 5.8 in 8 hours in the top 3 cm layer of peat resulted in a decrease of 50 % and 20 %, respectively, in the proportions of Cernosvitoviella briganta Springett and Cognettia sphagnetorum (Vejd.). The worm populations returned to normal following an increase of the I.H. values to 8.2, five hours later. In laboratory tests on mineral soils, 30 % of the worms moved downwards when I.H. values of the top 3 cm layer fell below 2.0.
Springett et al. (Thu,) studied this question.