The grey field slug, Agriolimax reticulatus (Muller), widely distributed in a variety of habitats (Quick 1960), is probably the most numerous species and the most important slug pest (Runham & Hunter 1970), although its status as a pest of permanent grassland is not known. South (1965) found average populations on pasture in Northumberland of over 60 per m2, aggregated in association with tufts of Dactylis glomerata L. No detailed investigation has been made of basic food requirements of this species and feeding in natural habitats has only so far been investigated in woodland (Pallant 1967, 1969, 1970). The diet of Agriolimax reticulatus, on grassland neighbouring on the woodland previously studied, was investigated by the analysis of crop contents. Prat (1932), Davies (1959) and Metcalfe (1960) used epidermal characteristics in the taxonomic study of grasses but Davies concludes that the distribution of differentiated cells over the leaf is of limited value for identifying a single leaf of a vegetative shoot and could only provide a 'broad analysis' of grass constituents of animal food. However, with a limited number of grass species available, it has been found possible to distinguish between them (Martin 1955, 1964; Croker 1959; Stewart 1967; Pollard & WaltersDavies 1968; Watts 1968; Bernays & Chapman 1970).