1927 ] The Social Parasitism of Harpagoxenus americanus 
3 
Table 1 gives the statistics for the 17 nests in which I have 
found Harpagoxenus. Numbers 3 to 9 were found in a small 
patch of woods near the village of New Vernon, numbers 10 to 
17 about four miles away, near Morris Plains. In the first 
locality 50 pure nests of L. curvispinosus were taken in July and 
August; in the second 30 were found in September, and at 
Belle Mead eight pure nests were taken on July 8. I have col- 
lected 27 pure nests of L. curvispinosus at various other localities. 
This gives a frequency of infection of 17: 132=13%. The fre- 
quency can hardly be as high as this over most of the range of 
Harpagoxenus, for the species would then hardly be so rare in 
collections. It is probably local in distribution, though my 
success in finding it in four localities suggests that it may be 
commoner in galls and old nuts than in hollow stfems, where the 
host has apparently been most often collected. I have taken 
only eight host colonies in hollo w stems (of sumac and hickory) ; 
none of these were parasitized. I have also taken three pure 
nests of L. longispinosus (one in each of the regions near Morris- 
town where Harpagoxenus was found and the third also near 
Morristown). None of these were parasitized. 
At least two of the nests in Table 1 seem to represent frag- 
ments of colonies. Number 3 had no Harpagoxenus workers or 
dealated queen, but contained six winged queens and one male — 
the mother of which was therefore not present. Number 7 
contained no Leptothorax at all. My observations agree with 
Wheeler’s that Harpagoxenus is quite unable to care for itself, 
so this colony must have had Leptothorax workers. Perhaps 
they were out foraging when I collected the hickory nut. Similar 
observations have been made on pure nests of L. curvispinosus: 
e. g., over 20 nests have been found that contained no queen. 
Accordingly I was led to test nests from nuts lying within four 
or five feet of each other on the ground. In two cases (pure L. 
curvispinosus) the individuals from such nests showed no hos- 
tility whatever to each other, over a period of several days, 
though they promptly and vigorously attacked workers from 
nests taken in different localities. In several cases (including a 
few parasitized nests) such experiments led to mild fighting, 
which often did not occur for several minutes after the introduc- 
