The life history and seasonal cycle of the ant, Pheidole morrisi Forel, as revealed by wax casting

Abstract

The dimorphic ant, Pheidole morrisi Forel, is the most common ant of the longleaf pine flatwoods ecosystem of northern Florida and occurs throughout the eastern USA. Although ecologically significant, its life history, and annual cycle have been little investigated. The effects of colony size and the annual cycle were described by collecting the full range of colony sizes during each of five seasonal phases (n = 40 total). Nests were cast in wax to capture and census all colony members, and to determine their vertical distribution within the nest. Colony sizes ranged from 800 to 49,000 ants, larger than previous literature reports. Colonies invested in worker production during the spring and fall and reduced worker production as they produced alates in the summer. Colonies over 3000 workers were able to produce alates, but the number was not related to colony size. Vertical distribution of nest volume was strongly top heavy, with the greatest proportion of the nest volume near the surface. The mean weight of majors was about four times that of minors. The mean percentage of total workers that were major workers (11 % by number, 30 % by weight) did not change significantly as colonies grew, but varied with season. Production of major pupae was highest in spring, so that the percentage of colony biomass represented by majors increased from about 27 % in spring to 38 % in late summer. The overall density of the ants was highest in medium-sized colonies, lowest in small colonies, and moderate in large colonies. Broadly, the colony moved lower in the nest from summer to winter and higher from winter to summer. The seasonal vertical distribution of ants suggested that the ants responded to temperature, but not crowding. Temperatures in the nest varied from 12 to 17 °C in the winter to 23–33 °C in the late summer. Broods were nearly always found in the warmest regions. The distribution of callow workers was strongly correlated with that of the brood. The results are discussed in light of the utility of the wax-casting method and the nature of the data needed to describe and understand the superorganism.