Dipteran larvae are known to infest turtle eggs. However, the few studies conducted on this topic have presented conflicting conclusions as to whether the larvae function as scavengers of necrotic nest material or as egg and hatchling predators. These two very different roles in the nest will have equally different effects on the subsequent hatch and emergence success of affected sea turtle nests. The association between dipteran larvae and sea turtle nest invasion was investigated by measuring rates of infestation in excavated green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtle nests at field sites in central Queensland, Australia. Excavations were performed within 24 h of hatchling emergence, and necrotic embryos and dead hatchlings were found to be infested with two larval species of the Platystomatidae: Plagiostenopterina enderleini and Duomyia foliata. This work represents the first description of the association between these dipteran species and sea turtle nests, and a new geographic collection record for D. foliata. High rookery infestation rates versus low prevalence of propagule infestation suggest that the larvae preferentially infest dead embryos. The fact that some pipped hatchlings were devoured in-shell presents the possibility that the larvae may act opportunistically as predators. However, the two dipteran species appear to be primarily scavengers of necrotic material within the nests, which means that the threat to sea turtle populations from these flies is probably minimal.