Bermudian Ants Revisited: The Status and Interaction of Pheidole Megacephala and Iridomyrmex Humilis

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Abstract
A survey of the distribution on Bermuda of the ant species Pheidole megacephala and Iridomyrmex humilis was conducted from August 6 to August 16, 1973. Based on 760 data points, Iridomyrmex appears to have established two new foci since 1966, one at Wreck Road and the other on the eastern end of St. Davids's Island, whereas Pheidole recaptured territory in the vicinity of Christ Church Leamington Caves, White Hill and Knapton Hill, the reclamation at the latter two sites begun in 1957 and 1963 respectively. Other than these changes, the overall distribution of the two species, as revealed in our survey, seems to be much more mosaic than seen in previous surveys. These observed changes in distribution suggest a need to reexamine the concept of the Iridomyrmex expansions as unidirectional. The fighting between Pheidole and Iridomyrmex that was occasionally observed probably took place at times when Iridomyrmex was attempting to expand its territory. Iridomyrmex was generally the aggressor and the victor. Baiting experiments were performed, the results of which indicate that Pheidole prefers clumped food resources, while Iridomyrmex prefers dispersed food resources. The potential for a partioning of the food resources suggests that the competition between Pheidole and Iridomyrmex is predominantly spatial. On the basis of our study, we believe an equilibrium between Iridomyrmex and Pheidole might be possible on Bermuda.

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