120 
Psyche 
[Vol. 88 
(i) the proportion of nests containing alates is more or less 
constant throughout the late summer, fall and winter, 
dropping rapidly in the spring; and 
(ii) there is a flush of colony-founding females in the early to 
mid-summer. To the extent that impressa and purpurea 
share the same seasonal cycle, it may be supposed that their 
nuptial flights also occur in the spring. 
Alates of confusa and chalybaea were observed actively dispers- 
ing or swarming on several occasions in rainforest and urban 
parkland in the Sydney region. All observations but one (out of 15) 
were made in the spring (September 15-November 10), and the only 
large-scale mating swarms were seen at this time. Most observations 
involved congregations of males around nest entrances. On six 
occasions, isolated male or female alates were observed away from 
the nest, apparently in a dispersing phase. Spring mating flights 
were observed for 3 consecutive years (1976-78) in the chalybaea 
population occurring on the University of Sydney campus. Because 
of the scarcity of information on this important stage of the life 
cycle, the 1976 mating swarm is described in detail. 
This flight took place on 4 October 1976, a mild overcast day with 
brief periods of sunshine and light rain. At the time observations 
were begun (10:15 a.m. EST) large numbers of chalybaea alates, 
mostly males, were observed flying in parts of the University 
campus. Alates were distinctly concentrated into clusters in tree- 
shaded areas. Three of these concentrations were examined in detail 
(Sites A, B and C in Figure 3). 
Site A. This cluster was centered about a chalybaea nest entrance 
between two slabs of sandstone which formed part of a stone wall. 
Between 10:45 and 11:45 a.m. there were several hundred males 
within 2 meters of the nest entrance. No alate females were seen. 
Although males spent most of the time on the ground chasing other 
individuals, the congregation appeared to be formed by males flying 
into the site. There were large numbers of workers milling around 
the nest entrance and most behaved aggressively towards the males, 
but this did not deter the latter from making repeated attempts to 
mate with workers (and with other males). Three apparently 
successful male-worker matings were observed; in each instance the 
pair was already in copulation when discovered, in a position 
similar to that described by Holldobler & Haskins (1977) for R. 
metallica. The worker dragged the male on the ground for about 30 
