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[Vol. 88 
(ii) as a result of colony fission or budding (hesmosis), in which 
one or more mated “workers”, accompanied by uninsemi- 
nated nest-mates, leave the parent colony to found a new 
daughter nest. 
As the foregoing remarks imply, there are two kinds of reproduc- 
tive females: queens and ergatoid (worker-like) gynes, the latter 
indistinguishable morphologically from unmated workers. This is 
the first record of reproductive workers in the impressa group (they 
are common and well-documented in some other Rhytidoponera ) 
where previous reports suggested that the only functional reproduc- 
tives were winged queens (cf. Brown, 1953, 1954; Haskins & 
Whelden, 1965). Mated queens and ergatoid gynes never coexist in 
the same nest, but they often occur in different nests in the same 
population (in confusa, chalybaea and impressa ). This rather 
remarkable dimorphism of female reproductives in the impressa 
group and the resulting differences in colony structure and genetic 
relatedness will be examined in more detail elsewhere (Ward, in 
prep.). 
There is little information on the frequency of colony fission in 
worker-reproductive colonies or on the size of newly-budded 
daughter colonies. Occasionally small isolated clusters of workers 
and brood are seen in the field, under stones or in rotten log cavities. 
Table 1 summarizes the composition of four such clusters in the 
impressa group, and two from other Rhytidoponera species ( tas - 
maniensis and fulgens). Similar observations were made by Haskins 
& Whelden (1965) on R. metallica. Note that in the two cases where 
workers were dissected (Table 1), only one individual in each cluster 
was found to be inseminated. In no instance in the impressa group 
(or in any other Rhytidoponera species) was a single isolated 
worker, with brood, located in the field, in contrast to the frequent 
occurrence of single colony-founding queens (see below). 
The process of colony fission is observationally difficult to 
distinguish from the movement of a colony from one nest site to 
another, and the two events may be inter-related. Table 2 summar- 
izes observations made on colony movement in chalybaea and in 
three other Rhytidoponera species (outside the impressa group). In 
only one instance ( maniae ) was a single colony observed splitting 
into two nests, but the same event may have been occurring during 
the other observations, if some workers remained at the original 
nest site. 
