Abstract
The seasonal prevalence of fleas on Rattus rattus were studied at Fuchu, Tokyo, through consecutive 12 months, from March, 1955, to Feburuary, 1956. The fleas were Nosopsyllus fasciatus, Monopsyllus anisus and Leptopsylla segnis. Xenopsylla cheopis, Paradoxopsyllus curvispinus, Echidnophaga gallinacea and Tunga caecigea were not found during this survey. All the three species showed their top peak of prevalence in May 1955. The fleas are quite seldom during the summer season but after October the flea index gradually increases and showed a second peak in November. Therefore it seems that under the airtemperature between 10℃ and 20℃ the fleas may increase and decrease if the temperature ascend above 20℃.
