Crataerina pallida, the swift lousefly, is a species of biting fly in the family of louse flies Hippoboscidae. These flies are commonly encountered in the nests of the common swift (Apus apus) in Europe and Asia. Crataerina pallida is vertically transmitted ectoparasite, in that it is passed from parent host on to offspring. C. pallida are relatively benign, because their own species fitness will depend on successful reproduction of swifts. Evidence suggests that C. pallida had little if any effect on nestling growth or fledging success rate. *