1987] 
McCluskey — Circadian rhythm 
249 
Fig. 3. Same group of E. tuberculatum, in same artificial nest, as in Fig. 2. DD 
arena rhythm, following single exposure to light for 12 h starting Feb. 13 at 2000. 
Day 2 = Feb. 15-16, 3 = Feb. 16-17, 5 = Feb. 18-19. 
This suggests a rhythm that is circadian in the strictest sense — 
internally controlled. The evidence stopped short of this for workers 
of the other two species studied simultaneously, Paraponera 
(McCluskey & Brown 1972) and E. ruidum (reported here); there 
was good rhythm in the lab, but no apparent persistence in constant 
darkness. However, in those two species, the colony fragment 
and/or hourly count of ants was much smaller; and this or other 
limiting conditions may well have obscured display of persistence. 
On the other hand, it should be noted that the male and female 
Paraponera studied at the same time did show a persistent rhythm. 
There is interesting field evidence for internal control of timing in 
workers of another BCI species, a leaf-cutting ant (Hodgson 1955). 
The ants were already in the nest openings an hour before dawn, too 
early for environmental cues of the approach of dawn; yet even 
strong light did not reveal them there or bring them forth at earlier 
hours of the night. 
For each species of Ectatomma the LD timing corresponded to 
that in the field. And in both field and laboratory, the two species 
were out of the nest at opposite times of day. If these particular nests 
are indeed characteristic of the species, we would see here an excep- 
tion to the general trend of similarity in rhythm among the species 
