What a hard working "mom" Yes, box turtles can and frequently do have multiple clutches of eggs. These eggs developed in her ovi-duct after the first clutch was laid. Since the summer is still young-she could even have another clutch! In the wild, the last clutch of hatchlings often over-winter in the nest chamber until spring. Good luck!
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Tess Cook
www.boxturtlesite.info