Nesting behaviour and embryo hatching success in spiny softshells (' Apalone spinifera') were investigated at two sites on Lake Erie. I recorded changes in nesting behaviour in response to human activity, rates of embryo hatching success, predation of nests by mammals, and determined the mechanism by which flesh fly larvae ('Tripanurga importuna') infest nests, and assessed the potential effect of fly infestation on nest success. I hypothesized that constraints on embryo hatching success, nest-site selection, and nesting behaviour limit reproductive success. Spiny softshells were readily disturbed by human activities (boating, walking on beach, etc.) during nesting. Mammalian predation was the most significant threat to embryo hatching success in both populations. 'Tripanurga importuna' is a habitat specialist, but also a food opportunist, able to find and develop on carrion or buried turtle eggs. 'Tripanurga importuna' maggots in turtle nests preferentially scavenge damaged turtle eggs, but will opportunistically prey upon live embryos and hatchlings under some circumstances.