CIRCADIAN RHYTHM IN THE TROPICAL ANT 
ECTATOMMA (HYMENOPTERA: FORMICIDAE)* 
By Elwood S. McCluskey 
Biology and Physiology Departments, Loma Linda University, 
Loma Linda, CA 92350 
Introduction 
In early 1960 I surveyed the daily activity rhythms of three tropical 
ponerine ants, Paraponera clavata, Ectatomma tuberculatum, and 
E. ruidum, first on Barro Colorado Island (BCI), Panama, then in 
the laboratory upon return home. The study of Paraponera was 
reported previously (McCluskey & Brown 1972). That of Ecta- 
tomma presented here is of interest in spite of being based on limited 
material, because it is one of the few studies of rhythmicity of ants in 
controlled conditions; the two species appeared opposite in time-of- 
day out of the nest, in both field and laboratory; and the rhythm of 
E. tuberculatum persisted in constant conditions. 
Methods and Materials 
All the observations for either species, whether field or labora- 
tory, were on one nest (except Fig. 1, field E. ruidum, two nests); 
hence the conclusions are based on replicate days, rather than nests. 
In the field, the best ant counts for the tuberculatum nest were on 
an adjacent vine, whereas the counts for ruidum were mostly on the 
ground. This accords with Levings & Franks’ (1982) statement that 
E. ruidum forages mainly at ground level, whereas E. tuberculatum 
forages mainly at shrub level. Night counts were made by dim red 
flashlight. 
At the end of January workers from the tuberculatum nest and 
from one of the two ruidum nests were taken back to E. O. Wilson’s 
laboratory at Harvard. They were kept in a darkroom at a constant 
temperature of 27.5 ± 1.5°C. (The shaded ground temperature on 
BCI averages 25-26° C all year [Levings 1983].) In alternating light 
and darkness (LD) there was fluorescent light, 400 lux, for 12 hours 
* Manuscript received by the editor June 24, 1987. 
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