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Psyche 
[Vol. 85 
The ants were identified by E. O. Wilson, and voucher specimens 
deposited in the collection at the Harvard Museum of Comparative 
Zoology. Colonies thrived and produced brood in artificial nests 
made of glass tubing of 5 mm diameter (approximately that of twigs 
in which wild colonies have been found (Jayasuriya 1979), and fitted 
with moist cotton plugs. Colonies were maintained at 26°C while 
observations and experiments were carried out. 
As is typical of this genus, P. hortensis has a completely dimor- 
phic worker caste. And, as is true for many ant species in general, 
newly eclosed P. hortensis are quite light in color, and darken as 
they age. Using the method first described by Wilson (1976a), we 
found that based on these color differences and the degree of pig- 
mentation of body parts each physical caste could reliably be sepa- 
rated into five color or age classes (see Appendix I). Using the obvious 
size and color differences, ethogram data on workers of different 
ages was compiled from 24 hours of observation on one colony over 
a ten week period. 
The nest tube and surrounding area were watched, and every 
observed act was noted along with the age class and physical caste of 
the ant performing it. During the 24 hours of observation 3,689 acts 
of 25 behaviors were recorded for minor workers, and 256 acts of six 
behaviors for majors. At the end of the study the colony consisted of 
192 minors, 32 majors, brood, and the queen. 
Data Analysis 
Completeness of the behavioral repertory was assessed by statisti- 
cal comparison with a lognormal Poisson distribution (Bulmer 
1974, Fagen and Goldman 1977). 
The hypothesis of age-based division of labor was tested with a 
standard comparison between observed performance frequencies 
by each age class for behaviors, and expected frequencies generated 
with the following formula (Altmann and Altmann 1977): 
(Bi)(nj) 
Ejj = Expected frequency of Behaviorj by age classj 
Bj = Observed frequency of Behaviorj by all age classes 
n; = Number of ants in age classj 
N = Total number of ants in all age classes combined 
