Monogyne fire ant colonies defend a foraging territory against their neighbors. The area of this territory is positively related to the size of the colony, but colony size is itself not a simple function of age. Rather, colonies generally grow to a maximum size, then, as they produce sexuals, begin to lose size year by year, losing territory in parallel. As they age, colonies devote a decreasing proportion of their workers to foraging. Thus, the density of foragers in the territories of small, young colonies is 3 to 4 times higher than in those of larger, older colonies. The resultant greater outward “pressure” of the forager populations of small colonies as compared to large may be the mechanism bringing about the loss of territory by large colonies.