Abstract
Within-colony variation in head width was measured for the species of ants found on the summit of Devils'' Tower (northeastern Wyoming) and for comparative study plots of similar size at the base of the tower, on the surrounding plains, and on the summit of an adjacent butte. Foragers of the species found on the tower had larger heads than foragers of the species found on the other study plots. The within-colony coefficient of variation in head width was also greater for the ant colonies on the tower than in the other study plots. An inverse relation was found between the % variation in head width within colonies and the number of coexisting species.