Ectoparasitism of nestling House Wrens, Troglodytes aedon, by larvae of the blow fly Protocalliphora braueri (Diptera: Calliphoridae)

We provide the first detailed information concerning ectoparasitism of nestling birds by larvae of the blow fly, Protocalliphora braueri Hendel. This species is unusual among Protocalliphora because its larvae cause a subcutaneous myiasis in small birds. We examined the pattern of infestation, and the effect of parasites on nestling survival and body size at fledging in a population of House Wrens, Troglodytes aedon. Twenty-five of 71 nests (35%) in the population were infested. Infested nestlings hosted an average of five larvae each. Myiases occurred in virtually all parts of nestling bodies, and larvae were visible on hosts for approximately 3 days. Parasitism did not appear to affect nestling survival if larvae appeared after the nestlings were approximately 6 days old. Some young infested at ages younger than this appeared to die as a result of parasitism, but infestation at these ages was rare (only 12% of nests). Comparison with other studies of dipteran ectoparasitism suggests that in most cases, parasite loads in our population are generally too low to have any significant effect on nestling survival. We also found no relationship between the intensity of parasitism and the tarsus size of nestlings at the time that they fledge, as measured by tarsus length.