40 
Psyche 
March 
Around their nest entrance, at some distance, circled a 
few Aphaenogaster workers, mostly each carrying one of 
their own larvae or pupae. Their behavior resembled that 
of Formica slave species when being raided by F. subintegra. 
Also running in the general vicinity of both nests, but 
not seen to participate directly in the raid, were a few 
workers of Formica fusca ( s . lat .), all of them slave mem- 
bers of the F. subintegra colony. 
The raid was under observation for about one hour, and 
my impression was that it had been in progress for some 
time before I first saw it. It compared with the terminal 
stages of other raids I have seen F. subintegra make on 
other Formica species. The raid was terminated by heavy 
rain in the early evening, and was not continued on the next 
day. 
On partial excavation, pupae and dead or injured workers 
of A. rudis were found in the subintegra nest, but there 
were no Aphaenogaster workers present and intact that 
seemed to be acting as slaves. Therefore, I concluded that 
the raid would probably not be successful in introducing 
the Aphaenogaster into adult slavery. 
In the present observation, it is not known whether the 
captured pupae or adult Aphaenogaster workers were eaten 
by the Formica raiders. But even if they were, such behavior 
is not necessarily of more than routine significance, since 
ants will eat their own pupae under various circumstances. 
My own interpretation of the raid is based on the apparent 
lack of nests of suitable slave species of Formica in the 
campground, and the abnormally exposed nature of the 
Aphaenogaster nest. Since F. subintegra workers had been 
seen foraging singly over the area for several days previous 
to the raid described, I suspect that these represented scouts- 
that were unsuccessful in locating suitable Formica spp. 
nests to plunder. Under such conditions, the pressure for 
the release of raiding activity may have been high, so that 
eventually even such a poor target as the Aphaenogaster 
nest came to represent a stimulus sufficient to start and 
maintain a raid. 
