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[Vol. 91 
be the primitive caste and minor workers the novel caste. In Pro- 
cryptocerus, workers closely resemble the queen as do soldiers in 
Zacryptocerus and large workers in Cephalotes. Advanced cepalo- 
tines appear to have added smaller workers to their worker caste 
systems. Soldiers of Zacryptocerus fulfill the first of two criteria 
proposed in Wilson ( 1980) for a primitive caste: they resemble the 
workers of the less modified, monomorphic members of the same 
tribe (e.g. Procryptocerus). Zacryptocerus soldiers do not meet the 
second criterion, that the primitive caste perform the generalized 
services of a colony. Wilson (in press) has discovered that Pheidole 
soldiers can be induced to express behavior typical of a minor 
worker’s repertoire; morphological specialization does not preclude 
behavioral flexibility. This discovery uncouples morphological and 
behavioral specialization and may relax the need for a primitive 
caste meeting the second criterion of generalized behavior. 
Ecological Similarity 
Ecological similarity between species can contribute significantly 
to similarities in behavioral traits. Cole has demonstrated that two 
species of ecologically similar but phylogenetically distant species of 
ants, Z. various (Myrmicinae) and Co/ohopsis sp. (Formicinae) 
exhibit convergence of qualitative behavioral traits as well as of 
quantitative aspects of their repertoires. Both species inhabit hollow 
twigs of a variety of plants that represent dry habitats (Smith, 1923; 
Kempf, 1958; Cole, 1982). 
Z. various and P. scahriuscu/us are also ecologically similar. Both 
nest in hollow, dry twigs, and the ants themselves are of similar size. 
In Z. various, minor workers measure 3. 6-4. 7 mm and soldiers 
5. 9-6. 3 mm in total length (Kempf, 1958). The size of P. scabriuscu- 
lus workers falls between the two castes of Z. various, with workers 
measuring 4. 6-5. 2 mm in total length. The colony size of both spe- 
cies is also small, not exceeding several hundred workers. In addi- 
tion, Z. various is known to be nocturnal, and P. scabriusculus is 
believed to be nocturnal of crepuscular (Snelling, 1968). 
C. atratus, in contrast, is a large ant (8-14 mm total length), 
nesting in spacious cavities in living wood. Colony size is extremely 
large compared to other cephalotines, with about 12,000 workers in 
a mature colony. They forage diurnally. Corn (1976) suggests that 
many of the differences between C. atratus and Z. various might be 
based on the differences in nest site. Use of infrabuccal pellets as 
