1927] 
The Slave Raids of Harpagoxenus americanus 
17 
2:45 the first Harpagoxenus emerged the ledge was in the bright 
sunlight. After a short period of aimless wandering the Harpa- 
goxenus started in the direction of the raided nest. Its progress 
was slow and uncertain, and on several occasions it became lost, 
to judge from its haphazard movements. It entered the Lep- 
tothorax nest at 3:14, having required twenty-nine minutes to 
cover 3 . 35 meters. Five minutes later it emerged with a callow 
and began to retrace its steps. In so doing it passed close to a 
longispinosus worker. The later drew back at its approach and 
then stood perfectly quiet until the raider had passed, an action 
which I subsequently observed many times in the artificial nests. 
Despite the added burden the Harpagoxenus completed the 
return trip in twenty-two minutes, entering its nest at 3:42. 
Neglecting the preliminary movements after its emergence from 
its nest, and deducting the five minutes spent in the raided nest, 
the entire trip of about 6.7 meters had been completed by the 
Harpagoxenus in fifty minutes. This gives it an average speed 
of 13.5 cm. per minute. Compare this with Dr. Wheeler’s 
observations (*10) on the speed of Polyergus when raiding, viz: 
1 . 3 meters per minute. It is true that Harpagoxenus is a small 
ant, scarcely a third the length of Polyergus, yet its smaller size 
will hardly account for its discrepancy in speed. I recently had 
the opportunity to study the rate of movement of Iridomyrmex 
humilis, a smaller ant than Harpagoxenus, and found that under 
optimum conditions it moved at the rate of approximately 2.75 
meters per minute. Size, then, has little to do with the activity 
of an ant. If, as seems altogether likely, we can assume the 
correctness of Dr. Wheeler’s postulate, ('07) that the ancestors 
of dulotic ants were active, predatory insects; if from this con- 
dition dulosis arose as a refinement of active predatism; then we 
must regard an ant which, though a raider, is slow and clumsy 
of movement as one in which the dulotic instincts are nearing 
extinction. 
We now take up a series of observations upon ants in arti- 
ficial nests, which are of interest in that thejr suggest what takes 
place when the raiders first enter the nest of their victims. On 
August 20th, while collecting in a damp wood, Mr. Brandt Steel 
called my attention to what I at first took to be a mixed colony 
