304 
Psyche 
[December 
out, but those which the brush touched were injured by the dichloro- 
methane. Although there was great excitement on the nest; at no 
time was there any organization into a. raiding mass; instead, each 
ant followed the trail singly. A dichloromethan solution made with 
F. p. nitidiventris workers caused no reaction at all. 
On July 6, 1967, a successful raid on F. pf. nitidiventris was in- 
duced. Several days previously part of a colony had been dug and 
placed in a transparent plastic shoe box with a door made at one end. 
Workers excavated cavities in the soil and established their brood 
there. The box was placed 6 feet from nest M-26, and the Polyergus 
entrance was watched until ants began coming out. When there were 
25 to 30 Polyergus circling the entrance (4:20 PM), the F. p. 
nitidiventris door was opened and a pheromone trail was laid to it. 
Ants followed the brush as the trail was put down on the hard 
pebbly soil; and, as before, there was no organization into raiding 
formation but simply excited individuals running along the trail. 
There were perhaps 25 ants on the trail when the first one reached 
the box, entered, found a pupa, and started home. Almost immedi- 
ately 3 others entered and found pupae. Their arrival back at the 
home nest caused a great outpouring of ants, and soon there were 
about 100 in the box and as many more on the trail. All of the pupae 
and larvae were hunted out and removed. When many ants returned 
without booty, the line of outgoing ants began to thin. The whole 
raid lasted 25 minutes — 4 minutes to the taking of the first pupae, 
16 for removing all of the brood, and 5 more of hunting before giving 
up. 
Immediately after the induced raid the ants started out on one of 
their own. Two hundred and seventy-two ants took part in this raid, 
so the colony probably had most of its forces involved in the induced 
one. 
The difference between the induced raid and a natural one lay in 
the fact that the laid pheromone trail caused excitement and raiding 
action in individuals, while in a regular raid there was mass action, 
with a large group of ants leaving the nest together and staying in a 
compact group as they traveled along. 
CONDITIONS UNDER WHICH RAIDS OCCURRED 
Polyergus raids on the Reserve took place in the late afternoon 
but varied in time from colony to colony. The 0-26 colony raided 
early; its mean time for starting a raid was 4:21 PM EST (20 
raids), while the Lawn Nest’s mean was 5:36 PM (21 raids). In- 
dividual raids at 3 other colonies began at 4:50 PM, 5:08 PM and 
