380 
Psyche 
[December 
chemical and tactual interactions among all individuals in the colony. 
Since individual ants contact each other continually in the bivouac 
and in raiding and emigration columns, their thresholds of arousal 
for tactual stimulation may be very high. Effectively then, this low 
level of reactivity on the part of the ants makes the beetles’ typical 
pattern of foraging well adapted to the physiological state of the 
ants. Thus, although the beetles exhibited no specific adaptations for 
preventing the ants from becoming aroused, they were successful 
predators on the army ants’ brood and booty, because their contact 
with the ants did not result in the dissociation of the ant columns. 
Although our observations represent only a preliminary study, we 
feel that both H. latitarsis and H. ferrugineus must be added to the 
list of organisms important in the biotic environment of the army ant, 
N. nigrescens. During the present study, as many as 15 individuals 
of H. latitarsis and H. ferrugineus were found associated with each 
colony of army ants, and each beetle consumed approximately 10-30 
army ant larvae during every emigration. Since the nomadic phase 
of N. nigrescens lasts about 18 days, during which time colonies may 
emigrate up to 15 times, several thousand larvae might be consumed 
by the beetles during the nomadic phase of each colony. This repre- 
sents a substantial degree of predation. 
The queen of N. nigrescens lays approximately 30,000 eggs every 
30-35 days. This potential increase in the size of the adult population 
is offset mainly by mortality of workers during the predatory raids 
in other ant nests, and by myrmecophiles which feed on all stages of 
the colony’s brood. These myrmecophiles are specialized insect 
“guests,” adapted to live within the ants’ bivouac and to emigrate 
with the colony each night during the nomadic phase. Most myrmeco- 
philes associated with colonies of N. nigrescens are flies of the family 
Phoridae and beetles of the family Staphylinidae. Akre and Retten- 
meyer (1968) have shown that several species of these staphylinid 
beetles closely mimic army ant workers, and can easily follow their 
chemical trails. The carabid beetles, H. latitarsis and H. ferrugineus , 
by contrast, are not specialized myrmecophiles. We have never found 
them in any of the 1 1 army ant bivouacs excavated during the past 
three years, and they apparently associate with the ant colonies only 
at night. 
