3oo 
Psyche 
[December 
to exist there for io years (1956-1965) ; but the main observations 
concerned a larger colony, located about a mile away on grid 0-26 
and known since 1961. Raids of this colony were recorded during two 
seasons. In 1964, during 50 days of observation in June, July, Au- 
gust, and early September, 29 raids were seen ; and in the summer 
of 1965, during 54 days of observation, 34 raids took place. 
NEST STRUCTURE AND COLONY SIZE 
The structure of the compound nests seemed typical of the slave 
species F. p. nitidiventris t which usually dig a shaft into the ground 
and then excavate chambers from it at various levels. Shafts may be 
single or multiple and may extend as deep as 3.5 ft. Entrances to the 
nest (occasionally there are 2 to 5) may be inconspicuous in the 
grass or may be surrounded by bare excavated soil. 
On August 30 and September 1 (it rained all day August 31) 
of 1965, one Polyergus lucidus-F ormica pallidefulva nitidiventris 
mixed colony was dug. This nest lay near the top of a grassy slope in 
the sandy loam which is common on the Reserve. To judge by a raid 
seen on July 19, 1965, in which 258 workers took part, it was a 
medium-sized colony. Thirty-seven chambers were found, extending 
down to 30 inches and spreading around the central opening for a 
radius of 8 inches. Because of the lateness of the season, there were 
no larvae or eggs in the nest; and some of the winged ants had al- 
ready flown. The Polyergus lucidus population consisted of one 
queen, 291 workers, 299 worker pupae, 1 1 5 females, 407 males, and 
13 male pupae. The F. p. nitidiventris numbered 4,527 workers and 
9 worker pupae. Thus the mixed colony contained approximately 
5,662 individuals, and the count of 590 Polyergus workers (adult 
and pupae) gave a ratio of 7.7 slaves to each Polyergus worker. 
TYPICAL RAID ACTIVITIES 
The 0-26 colony had an almost bare nest area 18 X 18 inches 
across, because I had dug into it early in 1964. Generally there was 
only an occasional ant in sight here during the morning and none dur- 
ing the warm midday period. By early afternoon 2 to 5 Polyergus 
could often be seen circling about or running off into the surrounding 
grasses. Later^ as the sun slanted to the west and the nest came into 
flickering shade, more ants came out and stayed on the nest area, 
circling and crossing it in a zigzag running movement. Then, typ- 
ically, there would be an outpouring of ants until they covered the 
nest. As they milled about, they explored into the surrounding 
grasses for several inches. Gradually the group would begin to favor 
one side, pushing into the grasses a little farther but always running 
