Fire Ant Polymorphism (Hymenoptera: Formicidae): Factors Affecting Worker Size

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Abstract
Worker size distributions are apparently not homeostatically regulated in colonies of the fire ant Solenopsis invicta Buren. Pupae produced in artificially composed polymorphic, dimorphic, and small-worker colonies were not significantly different in either average size or frequency distributions. However, larger colonies produced significantly larger pupae. Average pupal size was tightly correlated with the logarithm of colony size all the way from single founding queens up to mature colonies with tens of thousands of workers. High larval density also resulted in significantly smaller pupae. The apparent lack of homeostatic control combined with the influences of colony size and larval density, suggest that fire ant caste distributions do not track short-term environmental contingencies. Nevertheless, the general relationship between worker size and colony size is almost certainly adaptive.