A collection of juveniles of S. emarginata angulata was made from Phragmites Flats, an area at the north end of Douglas Lake, Michigan on August 8, 1956. This was followed the next summer by two collections of snails of the same generation made on July 1 and July 29, 1957. The incidence of infection with larval trematodes was low in the first two of these collections, but was quite high in the third. Only infections of D. flexicaudum and P. muris were present in any numbers. Collections of the same snail species made in 1936 from exactly the same area had been examined for their larval trematode infections. In them there was a much higher incidence of larval trematode infection with a considerably larger number of species. The collection made on August 26, 1936 had 77.4 per cent larval trematode infections with 11 different species, while that made on July 29, 1957 had 60 per cent infection and 5 different species. The 1936 collection also had a large number of multiple infections, 42 double and two triple. The July 29, 1957 collection had only three double infections. It is suggested that the reduction in trematode infections is due to a reduction in the number of vertebrate hosts, especially water birds, that visit the beaches because of the greatly increased number of summer cottages.