Life History of the Invasive Big-Headed Ant Pheidole megacephala (Hymenoptera: Formicidae)

The African big-headed ant, Pheidole megacephala (Fabricius, 1793), ranks among the world’s 100 worst invasive alien species, yet its basic life history remains poorly documented. We combined laboratory rearing and field observations in subtropical China with light and scanning electron microscopy to characterize the morphology, development, caste differentiation and reproductive behavior of this ant across its life cycle. Larvae passed through three instars. Head capsule width separated the three instars, whereas setal morphology was both instar- and caste-specific, because worker- and soldier-destined third instars remained densely setose while reproductive larvae shed their setae and were nearly glabrous as prepupae, an external marker of caste fate before pupation. At 28 °C, non-reproductives developed from egg to adult in 28.73 ± 2.83 d with marked asynchrony, whereas reproductives shared the early schedule but required longer prepupal and pupal periods, totaling 37.60 ± 3.20 d. Caste production was seasonal, colonies were polygynous, and oviposition proceeded in discrete batches. Nests were cryptic and associated with moist, sheltered microhabitats. This first integrated life-history account identifies seasonal and microhabitat vulnerabilities that surveillance and control can exploit.