1927] The Slave Raids of Harpagoxenus americanus 21 
ed outside the cavity. During the next night the curvispinosus 
recovered a part of their brood but this was again taken by the 
Harpagoxenus. This see-saw possession of the brood continued 
until September 3rd., when it was ended by the death of the 
Harpagoxenus . At this time there were eight curvispinosus wor- 
kers still alive. They immediately occupied the cavity and 
resumed the care of the brood. 
Any interpretation of the facts just described may be 
criticized on the grounds that the ants were captive insects 
placed in artificial surroundings. I am convinced that their 
actions may be explained on just such a basis, viz: that they were 
captives, unable to leave the artificial nest. There can be little 
doubt that the actions of the Harpagoxenus constitute a “dis- 
possession” of the Leptothorax of their nest and brood. Never- 
theless this cannot be regarded as the founding of a mixed colony. 
With this in mind I examined the four Harpagoxenus individuals 
with the greatest care and can positively state that not one of 
them was an ergatoicl female, if one may judge by the absence of 
ocelli or a female type of gaster. Under such circumstances the 
most plausible explanation is that of an interrupted raid. A 
condition making the return of the raiders to their own nest 
impossible, in this case confinement in the artificial nest, is, I 
believe, the reason for such occurrences. I have already given 
reasons for believing that the vestigial dulosis of Harpagoxenus 
makes its raids, even under the most favorable circumstances, 
very precarious. The surroundings of the nest from which the 
raids described above took place were as nearly ideal as could 
have been wished. The distance between the two nests was 
comparatively short. The smooth rock surface with its scat- 
tered lichens offered a minimum of obstructions and a substrate 
which facilitated the progress of the raiders. Yet even here the 
Harpagoxenus had difficulty in finding their way to and from the 
raided nest and frequently lost their way. Under the less favor- 
able conditions of terrain which usually surrounds the colonies 
the chances for a successful raid would be greatly lessened. 
The initial entry into the raided nest is, as the above observations 
show, a difficult matter requiring much time. During the inter- 
val, perhaps several days, from the advent of the first intruder 
