This study reports the relationships between rainfall and ambient temperature with the abundances and prevalences of three species of ectoparasitic arthropods (viz, mites, blowfly larvae, fleas) in pied flycatcher Ficedula hypoleuca nests in three different breeding seasons. In addition to its effects on the growth of nestling pied flycatchers, weather conditions were found to determine patterns of abundance and prevalence of ectoparasites. Nest ectoparasites had detrimental effects on the fitness (nestling growth and survival until fledgling) of their hosts, although the effects and the identity of harmful ectoparasites varied across the years. Among the three species of nest ectoparasites, mites had the most consistent harmful effects on nestling growth. Fleas were detrimental in the more cold and rainy year, while blowflies caused nestling mortality in the warmer year. Different host-parasite interactions were present each year, most likely due to the effects or weather on the activity and timing of development of parasite populations.