1985] 
Moffett — Behavioral notes on Acanthomyrmex 177 
Majors of A.ferox are involved in attacks on intruding ants, and, 
as in A. notabilis, a role as seed millers is probable. During my 
limited observations on this species majors were not observed hold- 
ing or carrying brood. 
Majors probably never forage. In the captive colonies, majors of 
both species were invariably at the nest unless there was a distur- 
bance serious enough to cause the ants to disperse. The only major 
seen away from the nest site in the field was an emigrating A.ferox 
individual. 
Although seed milling has yet to be confirmed by direct observa- 
tion, this activity very likely represents a primary function of the 
major caste. Oster and Wilson (1978) point out that seed specialists 
tend to be monomorphic or at most weakly polymorphic, while ants 
that have a broad diet consisting only partially of seeds are most 
likely to be polymorphic, with an extreme miller caste. Strongly 
dimorphic Acanthomyrmex ants have diets composed of small prey 
and scavenged material as well as seeds, and thus adhere to this rule. 
In Acanthomyrmex only a very few individuals of the major caste 
are present in any one colony. Indeed, majors form only a small 
fraction (less than 10%) of the total worker population, even though 
the colonies as a whole are very small. This is as would be predicted 
on the basis of ergonomic theory (Wilson 1968, Oster and Wilson 
1978). Because the morphology of Acanthomyrmex majors is so 
specialized, they would be expected to be very efficient at those 
specialized behavioral acts which they do perform. Therefore, rela- 
tive to a species in which majors are anatomically less deviant from 
the minors, fewer individuals are necessary to perform the special- 
ized tasks. 
Ergonomic theory also predicts that the more specialized the 
anatomy of the major, the more specialized its behavior, and the 
more limited should be its behavioral repertoire (Wilson 1968, Oster 
and Wilson 1978). It is therefore somewhat surprising to find that A. 
notabilis majors, perhaps anatomically the most extreme majors of 
any dimorphic ant, perform at least five social behaviors, among them 
holding and carrying brood. 
Wilson (1984) has shown that in Pheidole , majors normally per- 
form a more or less restricted set of behavioral acts. However, they 
can expand their repertoire to nearly equal that of the minor 
workers if the ratio of majors to minors is increased experimentally 
to beyond a set threshold value. This occurred within an hour of the 
