, Volume 9, Issue 4, pp 247-256

Foragers of the harvester ant, Pogonomyrmex owyheei: a disposable caste?

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Summary

  1. Exterior workers of the harvester ant, Pogonomyrmex owyheei, were subdivided into forager, defender and refuse worker behavior roles (Fig. 2). Exterior workers comprised approximately 16% of the total colony population with interior workers comprising the remainder.

  2. An average of less than 10% of the total worker population foraged (Table 1). Studies of role changes comfirmed a general one-way progression from interior workers to defenders to foragers (Fig. 5). The average longevity of foragers was about 14 days. As interior workers progressed toward foraging, their dry weights declined approximately 40% (Fig. 3) and mandible wear increased (Table 2).

  3. Based on these results, we propose that P. owyheei has evolved a disposable forager strategy that tolerates high forager mortality. The large reservoir of interior workers required by this strategy may also inhibit the evolution of physically specialized interior worker castes.