The ponerine ant Pachycondyla (=Ophthalmopone) berthoudi Forel carries loads economically

The energy cost of running and carrying a load were measured in the termitophagus ponerine ant Pachycondyla (=Ophthalmopone) berthoudi. This ant species uses the individual foraging method in which there is no cooperation between the foragers in the search for or retrieval of prey items. The foragers also transport workers and brood between the nests of the polydomous colony. Pachycondyla berthoudi foragers ran voluntarily in a running tube respirometer at 25 degrees C. Some of the foragers ran in the running tube carrying their termite load, which enabled the metabolic costs of carrying immobilized prey to be determined. This included the costs of maintaining the prey in the mandibles and of stabilization during running. The minimum cost of unladen running was 165.9 J kg-1 m-1, while that of laden running was 136.1 J kg-1 m-1. The mass used to calculate the cost of laden running included body mass of ant and mass of load carried. Pachycondyla berthoudi foragers carry their loads very cheaply. Load carriage costs were calculated to be about 40% as much as body carriage per unit mass, which is the lowest yet found for ants. Low cost of load carriage could have been selected for in P. berthoudi due to its life history.