1987] 
Gordon & Holldobler — Harvester ants 
345 
Foragers are less likely to engage in confrontations than patrollers 
are, but they are subject to predation by horned lizards ( Phryno - 
soma spp.). Nest maintenance workers, which appear to be the 
longest-lived, stay closest to the nest. Their task is in some sense the 
safest of the three. In addition, nest maintenance workers may be 
younger than the others, if this species adheres to the usual sequence 
of age polyethism in ants, in which younger ants work inside the 
nest and then move on to exterior tasks. Nest maintenance workers 
may be in transition from interior tasks to exterior ones such as 
patrolling and foraging. 
There are two important sources of uncertainty in this study: the 
paint used for marking can wear off, and marked individuals may 
still be alive inside the nest. Both these factors would lead us to 
underestimate worker longevity. More extensive studies are needed 
to determine how the expected lifespan of a harvester ant worker 
depends on its task, and how mortality rates vary in different Pogo- 
nomyrmex species. 
Summary 
Exterior workers were marked in the field, in colonies of the 
harvester ants Pogonomyrmex barbatus and P. rugosus. Some 
marked workers survived up to about 30 days after marking. These 
results extend the known limits on how long an exterior Pogono- 
myrmex worker can live. It appears that longevity may depend on 
worker task, with the following tasks in order of decreasing longev- 
ity: nest maintenance workers, foragers, and patrollers. 
Acknowledgments 
B. Cuevas, K. Roth, M. Allinei and H. Graham provided invalua- 
ble assistance in the field. We thank N. Carlin for comments on the 
manuscript. The work was supported by National Science Founda- 
tion grants BNS-8701480 to D. M. Gordon, and BNS 8521575 to B. 
Holldobler. 
References 
Gordon, D. M. 1984. The persistence of role in exterior workers of the harvester 
ant, Pogonomyrmex badius. Psyche 91 : 251-265. 
Gordon, D. M. 1986. The dynamics of the daily round of the harvester ant 
colony. Anim Behav. 34 : 1402-1419. 
