1. The allometry of colony mass to territory area governs the total bi
omass of ants that a given habitat supports. This relationship serves
as an important link between the performance of individual colonies an
d the behaviour of populations experiencing density-dependent competit
ion for space. 2. Territory area, colony mass, and the numbers of ants
of each caste and developmental stage, were measured for colonies of
the fire ant Solenopsis invicta across a wide range of sizes. 3. Most
of the variation in territory area was explained by colony size, measu
red either by worker number, worker biomass or colony biomass. 4. The
nature of this relationship was linear in May, when colonies were near
their annual minimum size, but non-linear in November, when they were
near their annual maximum. Territories of a given size were occupied
by larger colonies in November than May, probably because in this satu
rated population the simultaneous increase in worker number in all col
onies occurred without room for territorial expansion. 5. Mound volume
, which can be quickly measured without disturbing the colony, provide
d a reasonable estimate of colony or worker biomass and explained most
of the variance in territory size.