Foraging and building in subterranean termites: task switchers or reserve labourers?

Task-switching between foraging and building in workers of Nasutitermes exitiosus (Termitidae), a subterranean, mound-building termite, was investigated using mark-recapture. Foragers were collected from wood-filled drums and marked with Nile blue, whereas builders were collected from the mound by damaging it and collecting the termites that were undertaking repairs; these were marked with Neutral red. Two protocols were followed: the first marked foragers first and then damaged the mound; the second reversed this order, with up to eight drums sampled for foragers over 80 days. In the first protocol, the number of marked foragers that had switched tasks to building (blue-marked workers found in mound samples), was small compared with the number of blue-marked workers that remained foraging (0.7% cf. 1.8% of marked workers). The number of builders that had switched to foraging (red-marked workers found in the first drum sample) was also small in both the first and second protocols (0.3% of original number marked). The numbers of blue-marked foraging workers in drums decreased over time, whereas those for red-marked workers increased. The average decrease in blue-marked workers was ~1.5 workers (first protocol) and 0.5 workers (second protocol), the average increase in red-marked workers was ~2 workers (first protocol) and ~2.4 workers (second protocol). These results indicate that relatively few termite workers switch directly between foraging and building, but suggest that a pool
of workers exists that could be directed readily to either task.