The prey and feeding frequency in free-living grass snakes was studied during 1993 and 1994 at a site in southern England. Individual snakes and common toads were recognized using PIT tags and a small number of adult snakes were radio-tracked over long periods to determine predation rates.
Grass snakes fed, almost exclusively, on common toads (adult, juvenile, and tadpoles). A positive correlation was found between prey size and snake size. Large snakes did not appear to prey upon small toads, although clearly capable of doing so.
Male and female snakes ate large meals (toads) approximately every 20 days between May and September, with females fasting for a period of about 45 days during gestation and egg-laying. After allowing for differences in the number and size of toads predated by male and female snakes, the mean amount of food consumed per day was estimated to be 2.3% and 1.6% of body weight.