1983] 
Calahi, Traniello, and Werner — Pheidole 
409 
“caste” and “subcaste.” Because the two treat their data differently, 
comparisons are difficult, but we suggest that the castes and 
subcastes of Mirenda and Vinson correspond to the discrete and 
continuous modes of Wilson. Mirenda and Vinson consider as 
subcastes “(a) groups of individuals within each caste whose 
behaviour is statistically but not completely differentiated from 
other such groups and (b) groups intermediate in behaviour between 
two or more castes, but not completely distinct from any caste” 
(1981, p. 417). Both descriptions, and especially the latter, seem to 
fit the criteria for a continuous caste system — overlap in frequency 
distribution of age classes performing various tasks — rather than 
the discrete system, characterized by an exclusive association 
between an age class and a group of tasks. If this correspondence is 
indeed correct, we may be that much closer to a functional under- 
standing of labor roles, spatial efficiency, caste, and how task per- 
formance of individual ants sum to performance of whole castes. It 
is also noteworthy that although Mirenda and Vinson do not 
address the question of spatial efficiency as such, their results show 
a strong correspondence between ant age, location, and “career,” 
their “role” analogue. 
Clearly there is age-based division of labor in Pheidole hortensis. 
It does not seem to follow traditional role patterns, nor is it obvious 
which pattern it does follow. Therefore, we suggest two factors 
which must be considered for P. hortensis in particular, and in 
studies of age polyethism in general: “atypical” behavior due to 
labor cohorts, and role performance. Both have been documented 
for physical castes (Oster and Wilson 1978); one for age castes 
(Oster and Wilson 1978, Mirenda and Vinson 1981, herein). Because 
of these specializations, we suggest that mean behavioral perfor- 
mances by age classes may not be sufficiently fine-grained for 
detailed ergonomic analysis, and that the study of behavioral spe- 
cialization and its ergonomic consequences requires bouts of con- 
tinuous observation of individually marked animals throughout 
their lives. 
Summary 
We present evidence for and describe age-based division of labor 
in the Indo-Australian ant Pheidole hortensis. Both the minor and 
major physical castes exhibit age polyethism, and in both castes age 
