398 
Psyche 
[December 
a recruitment trail. Artificial poison gland trails have the strongest 
recruitment effect. The available data do not allow us to suggest 
a species specificity of the recruitment pheromone. Nevertheless, a 
specificity may well be accomplished by additional chemical orienta- 
tion cues. 
Summary 
Since individual harvesting ants (Pogonomyrmex badius) usually 
collect scattered seeds, casual observations in the past have seemed 
to indicate a foraging system based on individual initiative and 
orientation. But in the experiments described here and elsewhere 
(Holldobler 1971), we have proved that P. badius uses recruitment 
pheromones released from the poison gland and orientation or hom- 
ing pheromones released at least in part from the Dufour’s gland. 
Recruitment of nestmates is initiated when scouting workers en- 
counter food sources too large to retrieve in a single homeward trip. 
Although the poison gland pheromone is distinctly more effective in 
recruitment, the possibility exists that the Dufour’s gland pheromone 
can play a supporting role, especially in the establisment of longer- 
lasting foraging trails. 
Acknowledgements 
The research reported in this article was supported by grants 
from the Max Kade Foundation and the National Science Founda- 
tion (Grant No. GB-7734). 
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