1927 ] The Social Parasitism of Harpagoxenus americanus 
5 
natural conditions they would presumably have left the nest 
entirely. The Leptothorax queen did not fare differently from 
the workers, and ultimately she was so maimed that she died. 
It seems probable that under natural conditions she too would 
have migrated. Battles occurred from time to time for several 
days, until most of the workers were more or less maimed. The 
Harpagoxenus queen showed interest in the brood only inter- 
mittently, but occasionally rested on it. New workers emerged 
in a few days, and on August 4 one of these callows was seen to 
feed the Harpagoxenus queen by regurgitation. The old wor- 
kers still attacked her, however, and she grew gradually weaker, 
until she died on August 10. 
If one may judge from this experiment, the fertilized queen 
of H. americanus enters a nest of pure Leptothorax and ap- 
propriates some of the brood. The workers and queen are at- 
tacked, and emigrate probably to find a new nest, taking much 
of the brood with them. The intruder is then adopted by the 
workers that emerge from the brood she has appropriated. It 
may be surmised that nests numbers 11 and 16 represent cases 
in which this has just happened. In each of these nests there 
was present a single dealated Harpagoxenus queen, with a few 
Leptothorax workers, but no Harpagoxenus workers or pupae. 
Nest number 10 constitutes the best evidence that H. 
americanus makes “slave raids, ’ for this nest contained, besides 
nine workers and a queen of Harpagoxenus, two different host 
species — 41 L. curvispinosus and eight L. longispinosus. Both 
Adler z and Viehmeyer have found nests of the European H. 
sublcevis that contained two host species, and they have argued 
that these could be explained only on the assumption that H. 
sublcevis makes raids. Wheeler (1905) found a mixed nest of L. 
curvispinosus and L. longispinosus (without a queen) . and 
argued that if Harpagoxenus parasitized such a nest the result 
would be like that observed by Adlerz and Viehmeyer, but 
would not be due to raids. Viehmeyer (1921) has now actually 
witnessed the raids of H . sublcevis, so there is no necessity for 
explaining away the “triple” nests of that species. It is to be 
noted that Wheeler ’|s mixed nest was taken at the same place as 
his Harpagoxenus nests: it therefore seems to be most probable 
