378 
Psyche 
[December 
ant activities ceased at dawn, the beetles often entered sheltered areas 
beneath rocks adjacent to the ants’ bivouac. Three individuals of 
H. latitarsis , marked with red dye while foraging in a column of N. 
nigrescens at night, were recovered during the following day by turn- 
ing rocks adjacent to the colony’s bivouac. However, no beetles have 
ever been found in excavated army ant nests. 1 
Six individuals of H. latitarsis and four individuals of H. fer- 
rugineus were removed from army ant raiding columns, and main- 
tained in the laboratory in plastic petri dishes. To observe predatory 
interactions between beetles and army ants, a beetle was removed 
from its “home” chamber, and introduced into a petri dish containing 
50 adult ants and 100-200 eggs, larvae or pupae. In this situation, 
individuals of both beetle species fed voraciously on all developmental 
stages of the army ants’ brood (Fig. 1). The beetles exhibited bouts 
of running and feeding, which were followed by periods of complete 
inactivity, lasting up to 20 minutes. Since the only shaded areas 
in the plastic chambers were beneath the inactive beetles, workers 
of N. nigrescens often deposited their brood in clusters beneath them. 
When the beetles again became active, they readily fed on these brood 
clusters. 
In the confined observation chambers, each period of feeding by the 
beetles aroused the ants to exhibit their “alarm” reaction^ which 
consisted of ants standing on their hind legs, opening and closing 
their mandibles. The ants also “attacked” the beetles by biting and 
stinging their antennae and legs (Fig. 1). However, these activities 
rarely disturbed the beetles, and although they are capable of secreting 
a defensive, repellent chemical (Eisner et al ., 1968), there was no 
indication that they had sprayed the ants with it. 2 
Discussion 
Although many species of carabid beetles are numerous in the field 
study area, and routinely forage actively at night, H. ferrugineus 
and H. latitarsis were the only beetles found with colonies of N. 
nigrescens . Whether they encounter colonies of army ants accidentally 
while foraging, or actively orient towards them, is not known. Lab- 
Trofessor Julian Watkins II has informed me that an individual of a 
related species, H. tcxanus, was uncovered in an excavated bivouac of N. 
nigrescens . 
2 Plsek et al. (1969) reported that an individual of H. texanus, confined 
in a plastic chamber with 100 workers of N. nigrescens , sprayed the ants 
that were attacking it. The repellent spray caused the ants to withdraw from 
the beetle. 
