The Habits and Ecology of the British Harvestmen (Arachnida, Opiliones), with Special Reference to Those of the Oxford District

1. The twenty-one British species of harvestmen have all been found in the Oxford district with the exception of Nelima silvatica. Seventeen of them have been found in Wytham Woods, Berkshire, where the main research was done. 2. There are three main types of life history found among the harvestmen. They may be found all the year round and have an overlap of the generations (e.g. Nemastoma lugubre); or they may be annuals which die before their eggs hatch. Of the annuals some hatch in the autumn and overwinter as immature forms (e.g. Platybunus triangularis and Megabunus diadema); others, including the majority of species, emerge in the spring and die off at the end of the autumn. 3. The numbers of harvestmen are never very large. In June, a maximum number of approximately 50 may be found in a square metre ground layer in deciduous woodland. The maximum biomass is found in July when there were more than 200 mg. of harvestmen per square metre in this habitat. 4. There are three main woodland species in Wytham Woods: Nemastoma lugubre found on the ground layer, Oligolophus tridens on the ground and field layer and Leiobunum rotundum on the tree trunks. 5. There is usually microhabitat separation in space and time, or both, of closely allied species of the same genus. 6. Harvestmen are most active at night. This activity is correlated with the decrease in light intensity, increase in relative humidity and decrease in temperature in the wood. 7. L. rotundum leaves the tree trunks at night and feeds on the field layer. It hunts on the under surface of Mercurialis perennis leaves. 8. There was found to be a strong correlation between the humidity preference of the species as tested in the laboratory and their stratification in oak woodland.