1. I examined how the Hippoboscidae Ornithomya chloropus is spatially and temporally distributed in an insular metapopulation of house sparrows in northern Norway from 2004-2011, whether there were demographic differences in abundance as well the relationship between abundance and morphology, and abundance and survival in juvenile house sparrows.2. I found a handling effect on the abundance of O. chloropus which reduced the number of flies found on individuals from their first to their second catch.3. There was considerable variation in abundance between years and islands as well as within seasons, and abundance of O. chloropus differed between age-classes.4. There was a negative relationship between abundance and the three morphological traits; body condition index, body mass and tarsus length. There was also a positive effect of age on these morphological traits and a negative effect of late hatch days.5. There was a positive relationship between juvenile survival and body condition index, and survival and tarsus length.6. These results indicate a relationship between the abundance of O. chloropus and the fitness of juvenile house sparrows with morphology while there was no clear relationship between juvenile survival and abundance.