The Natural History of the Arboreal Ant, Crematogaster ashmeadi

Abstract

The arboreal ant, Crematogaster ashmeadi Emery (Hymenoptera: Formicidae), is the most dominant arboreal ant in the pine forests of the coastal plain of northern Florida. The majority of pine trees harbor a colony of these ants. The colonies inhabit multiple chambers abandoned by bark-mining caterpillars, especially those of the family Cossidae, in the outer bark of living pines. They also inhabit ground level termite galleries in the bark, often locating the queen in galleries. The density of chambers and ants is highest in the base of the tree and drops sharply with height on the trunk. Because chambers are formed in the inner layer of bark, they gradually move outward as more bark layers are laid down, eventually sloughing off the tree's outer surface. Chambers have a mean lifetime of about 25 yr. The abundant chambers in pine bark are excavated by a small population of caterpillars and accumulate over decades. Ant colonies also inhabit abandoned galleries of woodboring beetles in dead branches in the crowns of pines. Because newly mated queens found colonies in abandoned woodboring beetle galleries in the first dead branches that form on pine saplings, C. ashmeadi is dependent on cavities made by other insects throughout its life cycle, and does little if any excavation of its own. Mature colonies nest preferentially in chambers greater than 10 cm2 in area, a relatively rare chamber size. In natural pine forests, this does not seem to limit the ant's populations.Founding queens containabout 50% fat and lose about half of their dry weight during the claustral period, converting approximately half of this lost weight into progeny. The claustral period is about 40 to 50 days at 27°C. Mature colonies contain several tens of thousands of workers (est. up to 80,000), and have a life expectancy of 10 to 15 years. Each colony occupies an entire tree, and sometimes two trees if they are close together. Within a colony, there is a single queen capable of laying up to 450 eggs/day during the warm season. Such queens weigh 12 to 18 mg, have 50 to 60 active ovarioles and 120 to 600 vitellogenic oocytes in their ovaries.Mature colonies begin producing sexual brood in late April or early May. Sexual adults are present from late May through June. Mating flights commence in June and most sexuals have left their natal nests by late July. Female sexuals are an especially large investment; the energetic content of a single, flight-ready female sexual is almost 20 times that of a worker. The newly mated queen sequesters a mean of 2.64 × 106 sperm in her spermatheca, a supply that should last her for 16 years at the observed reproductive rates.