The giant silk moth Callosamia promethea (Promethea Moth) overwinters as pupae in cocoons spun in hanging leaves. Even though they are camouflaged, moths at this developmental stage are vulnerable to parasitism and predation, both of which are relevant to local population abundance and persistence. Our study documented the fates of overwintering Promethea Moths near Weld, ME, during 7 winters from 1997 to 2017. Our collection and dissection of 923 cocoons revealed that moth emergence declined from 47% to 10% over the study period. Parasitism by 2 native species of ichneumonid wasp (Gambrus nuncius and Enicospilus americanus) was the dominant cause of mortality, accounting for 59% of Promethea Moth pupal death. Predation accounted for less than 4% of mortality. Our results provide evidence of parasitism as a major contributor to mortality of Promethea Moth pupae.