In a Danish spring the life cycle of Sericostoma personatum Spence (syn. S. pedemontanum Mac-Lachlan) took three years. A comparison is made with a I½ year life cycle reported by Elliott (I969). The poor quality of the food and lower temperature in the spring area are suggested as explanations of the difference. A slight growth retardation was found for all three year classes in winter and was referred to lower temperatures.