Features of the development of Stomoxys calcitrans (L.) are described, based on observations in Uganda on stocks maintained in laboratory culture at 80°F. and 80 per cent, relative humidity. Eggs hatch within 24 hours of deposition, and the mean viability of 10 random batches was 76·5 per cent. The larvae are about 1 mm. long when newly hatched, reach maximum length (about 11 mm.) in the third (final) instar on the seventh day, and pupate one day later, the puparium being barrel-shaped and about 5 mm. long and 11 mg. in weight. The pupal period is two days. Females mate when six days old and oviposit 1–2 days later. The mean values, for five newly emerged, once-mated females, of total eggs laid, number of batches and duration of egg-laying (in days) were, respectively, 376, 10·6 and 12·2.

To be suitable for breeding of Stomoxys in the field in East Africa, sites require the presence of rotted cattle dung, rotted straw or foliage, and shade. In the dry season, such conditions occur only within cattle enclosures and particularly in the small, grass-thatched structures, provided with straw bedding, that are used for housing calves. In the wet season, suitable breeding conditions occur in open park-land and banana plantations, wherever rotted cattle manure and vegetation occur together.