Studies on the duration of the oviposition and incubation periods of Boophilus decoloratus (Koch, 1844) revealed that these non-parasitic periods are temperature dependent, increase in temperature causing shortening of the periods. Humidity had no effect on the duration of either the oviposition or the incubation periods. The relation between the mass of engorged female ticks and that of the eggs they produced was found to be linear. The viability of eggs produced during the first 13 days of oviposition (at 26 °C) was greater than that of eggs laid subsequently. The critical temperature for B. decoloratus eggs was found to be 42 °C and they were shown to be unable to take up water vapour from damp atmospheres. Both temperature and humidity affected the hatch of eggs. A simple model of the relations between the physical factors of the environment and the various biological phenomena studied has been given.