Observations have been made on the survival of unfed rat-fleas, both newly hatched and wild-caught, under controlled conditions of temperature and relative humidity, and further observations on oviposition, hatching of eggs and emergence of adults under the same conditions.

The results show that, of the three sets of conditions employed, a temperature of approximately 20° C. and relative humidity of about 100 per cent. are the most favourable for survival of adults, hatching of eggs and production of a further generation of adults. The two other sets of conditions (temperatures of 15 and 30° C., with relative humidities of 60 and 100 per cent. respectively) are entirely unsuitable for the breeding of the species of fleas used.

At 20° C. and relative humidity 100 per cent. the whole pre-adult life of Xenopsylla brasiliensis and X. cheopis is, on the average, approximately 8–9 weeks, the minimum being 6 weeks. The female in both species is shown to have a distinctly shorter larval and pupal life than the male.