Climate change threatens bird populations around the globe, influencing aspects of life history, survival, and parasite-host interactions. Breeding-season cold snaps factor into such changes, having become more variable, frequent, and intense (Shipley et al., 2020). In this study, we aimed to uncover how climate change may affect host-parasite interactions through examining the effects of cold snaps and elevated corticosterone on blowfly (genus Protocalliphora) presence and development in Tree Swallow (Tachycineta bicolor) nests. We simulated cold snaps and non-invasively increased adult female corticosterone levels in two different experimental groups, and then measured the abundance and size of blowfly pupae in response to these treatments. We hypothesized that both temperature and adult hormonal profile influence the presence of blowfly pupae in Tree Swallow nests. We predicted that 1) cold-treated nests would be more likely to contain blowfly pupae and have pupae of smaller size than control nests, and 2) corticosterone-treated (cort-treated) nests would be more likely to contain blowflies and have pupae of larger size than control nests. Our results did not support the hypothesis that both temperature and corticosterone influence blowfly presence in Tree Swallow nests. Cold-treated nests were not more likely to contain more blowfly pupae, nor had pupae of smaller size than those in control nests, and cort-treated nests did not contain more blowfly pupae or pupae of larger size than those in control nests. This lack of effect of parental corticosterone or cold snaps on nest blowfly presence or size points to the need for future studies testing more direct pathways of this and similar systems. Much remains unknown about the impact of corticosterone and temperature on the presence and size of blowflies and other avian ectoparasite species that may be more affected by such variables. The mechanisms behind such interactions are likewise unknown, though this study indicates that the timing of cold snaps within host and parasite life cycles likely contributes to the severity of infestation. This and future research on the topic aim to understand how species interactions with resources and each other change within our rapidly changing environment.