It has not been previously stated that Kerteszia are anophelines a slow development. Even the researchers that have bred those mosquitoes, took the delay observed in the development of the larvae as resulting from inadequate techniques. From an analysis of the data concerning monthly collections of larvae and adults, carried out in the State of Santa Catarina, Brazil, it resulted: 1. The mortality in the period from oviposition to the first ecdysis, is ca. 90% and in the first stage, probably is not lower than 75%; 2. At least during three months the percentage of the breeding biotopes with first stage larvae is lower than 35%, a fact which may be observed only in populations of insects of slow development; 3. The percentage of breeding biotops with first and second stage larvae has its maximum value in autumm; on the other hand, the ones with larvae in the third and fourth stage, predominate in the winter; 4. In the only forest where the periodicity of the breeding biotipes showing pupae was statistically significant, the greater percentage of these breeding places was found in the spring; 5. The fact that the breeding biotopes with first stage larvae are more abundant in the autumn, a time during which activity of the adults is low, and that the ones with fourth stage larvae are more abundant in the winter, seems to show that the eggs laid at the end of the summer do not achieve their development in less than four months; 6. The presence of pupae during the whole year shows that the adults emerged without discontinuity; 7. Two sudden increases of adult desity, one in September and the other in January, seem to show that: a) The Kerteszia from the winter, and the ones which survived from the precedent season, have their activity reduced in the cold and only begin to be eager for blood with the first waves of warm air of the spring; b) The laying of the eggs, achieved in September will only give adults at the end of December, namely ca. four months later. 8. After studying different factors which may induce delaying of the development of mosquitoes, it was concluded that the slowness of growing showed by the Kerteszia larvae, results of their evolution in an habitat permanently stabilized, such as the water biotopes in the Bromeliaceae, where the food defficiency is permanent; 9. The fact that all Kerteszia species are of a small size is also favorable to the precedent conclusion. The data upon which this work was done were gathered from fieldnotes kindly supplied by Dr. Henrique P. Veloso.