Females of Boophilus microplus on British breed steers were counted regularly from July 1971 until January 1974 at Mt Tamborine, a cool and moist habitat in south-east Queensland. Larval production was estimated by exposing engorged individuals in pasture at regular intervals. Three generations of ticks fed on the cattle each year, starting in late-spring and ending in late-winter. Much greater numbers of ticks in 1973 than in 1972 were attributed to higher summer and autumn temperatures. These accelerated development and increased the length of the period during which eggs could hatch and give rise to a larger third generation of parasitic ticks. The results illustrate the highly variable sizes of tick populations within and between years in such marginal habitats and the overriding importance of temperature as a determinant of that variability.