132 
Psyche 
[December 
land confines the nest building to the narrow strip along 
the forest margin. It thus exerts a negative or phohibi- 
tive influence which prevents the further spread of the 
mounds into the open where similar sunlight intensity pre- 
vails. It may be further noted in this connection that the 
greater number of mounds in the open are of the small 
type, the galleries of which do not extend far below the 
surface of the ground. Inspection shows soil conditions, 
other than moisture, to be quite similar in various parts of 
the area. There has been little erosion or deposition and 
the morainal drift is uniform in character. The ants build 
mounds and subterranean galleries with facility in both 
the loose surface soil and the hard clay below. 
The relation between the presence of a colony and dam- 
age to surrounding vegetation has not been studied but a 
possible correlation is suggested in the well developed clear- 
ing surrounding all colonies in the interior of the forest. 
Andrews (1928) reports damage of mound building ants to 
vegetation. In this instance, however, consideration of the 
light conditions and the complete absence of either mounds 
or clearings in the denser parts of the forest indicate that 
the clearing is a cause rather than an effect of mound pres- 
ence. 
An interesting aspect of the problem not yet investigated, 
is the extent to which Formica ulkei modify the fauna of 
the region, or the extent to which certain species are absent 
or present here in comparison to similar areas not so popu- 
lated by these ant colonies. Finally, observations on the 
unequal activity of mounds of the various sizes recorded in- 
dicate the need for careful analysis of the relations between 
size, age, and population of ant mounds. Such an analysis 
depends on subsequent periodic observations of these 
mounds, announcement of which will be made when their 
significance becomes apparent. 
Summary 
1. A survey of Palos Park, Illinois region records the 
presence of 435 mound-nests of Formica ulkei Emery in an 
area one quarter mile square. 
2. Measurement of light intensity with the Macbeth II- 
