Three times annually over a 5-year period, we mapped and measured over 1000 fire ant colonies distributed among 12 plots in a large cow pasture in northern Florida. Using mound volume as a surrogate for colony size, we tracked hundreds of colonies from infancy to maturity and old age. Colony growth in this mature population was highly variable, but followed a general pattern of growth for 3-4 years, followed by decline. Turnover rate and life-table calculations showed mean colony lifespan to be about 7-8 years, with a few colonies surviving as long as 11 years. Mortality rate declined for the first two years of life, and began to increase again after the 4th year. Population age/size structure was always right-skewed. Appearance of new colonies was always highly seasonal, but varied significantly across years. Colony size distributions were such that a very small proportion of colonies produced a very large proportion of the total sexuals in this population.