The cyclic biting activities of East African mosquitos of the genus Aëdes, belonging to the subgenera Mucidus, Diceromyia, Finlaya and Stegomyia are discussed. The total number of 24-hour catches involved was 448, all in East Africa, of which 401 were made in forest in Uganda.

It is pointed out that many species in the subgenera of Aëdes dealt with show arboreal tendencies of varying degree and, while a species may show a preference for some particular level, many of them appear to make daily vertical migrations. Consequently, biting may reach its maximum intensity at different times at different levels. It is also pointed out that the habits of a species may vary from one area to another, and therefore it is often best to discuss a representative series of catches from a productive area, noting such differences as may have been observed elsewhere. It has been found further that, under certain circumstances, a species may fail to show a clear pattern of biting behaviour and the possible reasons for this are discussed.

All members of the subgenus Mucidus so far adequately studied are arboreal and nocturnal. In the subgenus Finlaya, A. ingrami Edw. is a mosquito of the forest understorey which bites most freely in the hour before sunset. It makes vertical migrations, however, and the biting cycle at ground-level differs from that in the trees. A. longipalpis (Grünb.) is a diurnal species of the forest canopy. A view formerly put forward by the writer, that the form of the biting cycle in this species could be attributed to different physiological groups biting at different times, can no longer be supported.

In the subgenus Stegomyia, A. dendrophilus Edw. and A. apicoargenteus (Theo.) are diurnal species with rather irregular biting cycles, A. dendrophilus