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Proterometra macrostoma is a digenetic trematode that is widely distributed in the eastern United States. The objective of this study was to assess how the cercariae of P. macrostoma within their redia in the infected intermediate snail host (Elimia semicarinata) respond during an initial 7-d exposure of their snail host to 20°C (mimicking a fall temperature), followed by a cold-water exposure of 7.5°C over a 28-d period (mimicking a winter temperature), and within a week after returning to warmer water at 20°C (mimicking a spring temperature). Specifically, we investigated whether cercarial development inside the redia ceases or continues during exposure of the snail host to a winter temperature, which was determined based on changes in the cercarial composition in each redia in the infected snails and the amount of cercarial shedding. Naturally infected snails (E. semicarinata) were collected from North Elkhorn Creek, Scott County, Kentucky, during June and July 2019. Baseline cercarial emergence was recorded over 7 d at 20°C for 55 snails with patent infections. Infected snails were then maintained at 7.5°C for 28 d and checked daily for any cercarial emergence followed by a post–cold treatment analysis of cercarial emergence over 7 d at 20°C. No cercariae were released during the 28-d cold treatment. Significantly more (mean ± SE) cercariae were released per snail during the 7 d following the cold treatment (4.60 ± 0.33) compared to the period prior to cold treatment (3.63 ± 0.35). At the termination of the experiment, 94.6% of infected snails were found to have living rediae with a mean ± SE infection intensity of 7.13 ± 0.51 rediae/snail (range 1–18). Additional sets of snails (pre–cold treatment = 4 snails; post–cold treatment = 5 snails) were dissected at the beginning of the pre– and post–cold treatment periods to observe individual cercarial populations within rediae. No significant differences were found in the average number of the 4 cercarial stages described within rediae pre– vs. post–cold treatment. These results suggest that additional cercariae within rediae mature during winter months, but this was not detectable by our staging criteria. [ABSTRACT FROM AUTHOR]