1929] 
Myrmecocoles of Formica ulkei 
207 
area “A”, as if these unfortunates had run about until 
exhausted in the dry atmosphere, and had returned to die 
in the originally moistened area. 
A fourth petri dish, with no filter paper over the bottom, 
was used as a partial control and the two leptinids therein 
were normally active throughout the experiment, hiding 
in the loose soil covering the bottom or walking over the 
glass sides of the dish. It is doubtful if the presence of the 
filter paper, rather than moisture, was the cause of the 
behavior of the experimental animals, especially since in 
these latter cases, the dry areas of the filter paper acted 
as a partial control as well as the dish with slightly 
moistened soil. 
The above experiment was repeated with testaceus with 
the same results, and also with Batrisodes. In the case of 
the pselaphids, ten were placed in a petri dish, instead of 
two leptinids. Random walking about was observed for an 
hour, and then with the moistening of the filter paper at a 
definite point as before, the pselaphids soon found this 
area, and a few minutes later were motionless in the center, 
viz. the moist wet portion of the filter paper. The large 
number of the pselaphids made possible the use of larger 
groups in the experimental dishes, and the beetles were 
seen to aggregate in the center of the moist area. Usually 
this place aggregation was motionless, relatively, the beetles 
resting quietly on the paper, frequently with their legs and 
antennae touching each other. Such an aggregation reminds 
one of the bunching of land isopods under similar condi- 
tions (Allee, 1926, 1927), and may be partially explained 
as a contact aggregation in which the limited moistened 
area and subsequent crowding formed the aggregation. On 
the other hand, the pselaphids, Batrisodes globosus and 
denticollis, may very well exhibit a normal tendency to 
collect in pockets or portions of galleries of their host’s 
mound. In either case, a relative amount of moisture may 
be cited as an important stimulus. 
As in testaceus , the pselaphids, when left over night on 
the drying filter paper, were found dead the following morn- 
ing, loosely bunched on the center of the previously moist- 
ened section. 
