The life cycles of many species of Diplostomum (Digenea) have been elucidated; however, few studies include the details of egg development and hatching success. Here the eggs of 2 molecularly delineated sympatric species of Diplostomum were observed for differences in developmental parameters. These parameters included prepatent period, time required for first visible eyespot formation, hatching time, and hatching success. There was no significant difference in the mean prepatent period, total number of miracidia that developed eyespots, or number of days to hatch between the 2 species. There was a significant difference in the average time for first visible eyespots to appear and hatching success. These data highlight the need for further studies investigating sympatric species of Diplostomum to document and understand differences in life history traits during the various phases of their life cycles and their role in transmission success.