Seasonal dynamics of Ceratophyllus hirundinis (Curtis, 1826) (Siphonaptera, Insecta) in the nests of Delichon urbica (L.). The annual cycle of C. hirundinis was studied in 61 nests of Delichon urbica. Fleas were found in the 45 nests. In the number of adults two peaks were observed, the lower in March and the higher in October. Females outnumbered males throughout the year.