100 
Psyche 
[Vol. 88 
victoriae is considerably smaller than the impressa group species, 
and nests preferentially under stones. 
In some north Queensland localities, purpurea or impressa 
coexist with one of several small Rhytidoponera species (e.g. 
chnoopyx and kurandensis nesting in logs and under stones) and 
with one of several larger species (scaberimma and related species, 
nesting in logs and directly in the soil). There are no rainforest 
Rhytidoponera of comparable size to the impressa group species 
that regularly coexist with the latter with the exception of croesus 
(s.l.), which nests in rotten logs and in tree trunks in rainforest and 
wet sclerophyll of New South Wales and southern Queensland. R. 
croesus appears to be generally uncommon, and in fact averages 
slightly smaller than chalybaea, confusa and impressa to a degree 
which may significantly reduce prey size overlap (see below). 
Colonies of other Rhytidoponera species are virtually never 
found occupying the same nest site as an impressa group colony 
even though other medium to large ponerines such as Amblyopone 
australis, Leptogenys hackeri and Prionogenys podenzanai are 
occasionally found nesting in close proximity to an impressa group 
colony (e.g. under the same stone, or in adjacent cavities in a log). 
Colony Movement 
It appears that species in the impressa group are prone to move 
colonies from one nest site to another rather frequently. For 
example, in one rainforest population of confusa (Royal National 
Park, N.S.W.) eight stones under which colonies had been briefly 
located and otherwise left undisturbed were examined one week 
later: half were unoccupied. Three weeks later, only two colonies 
remained under the stones. While the censussing no doubt consti- 
tuted a disturbance conducive to nest-movement, it demonstrates 
nevertheless the readiness with which colony movement is carried 
out. 
During the course of field collections, vacated nest chambers were 
occasionally encountered (under stones or in rotten logs) whose 
previous occupants could be traced to an impressa group species on 
the basis of cocoon remains in the middens. Moreover, colony 
movement involving transport of brood and other workers was 
observed several times in chalybaea (and in other Rhytidoponera 
species outside the impressa group) (Ward, 1981). 
