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[December 
active only during the first half of the light period, whereas the 
workers were active only through the night. In Iridomyrmex humilis 
in LD the males come out only for the last hours of the light period, 
whereas workers are seen out at all hours (McCluskey, 1963) ; in- 
side the nest, however, males are active at least throughout the day- 
light hours (McCluskey, 1965). In V eromessor andrei , the males 
are active mainly around the dawn in LD (McCluskey, 1958), the 
peak for the females is then but activity is spread over many hours 
(McCluskey, 1967), whereas the broad peak for the workers is 
around dusk with activity spread over many hours (McCluskey, 
1963, and unpublished). 
The nature of the caste difference in rhythm deserves further 
study with respect to its import for both comparative and social be- 
havior, as well as for interaction with the natural cyclic environment. 
Summary 
Few laboratory studies of circadian rhythms have been made in 
social insects. Ants from one nest of Paraponera clavata were studied. 
In the field on Barro Colorado Island they emerged regularly at 
dusk and apparently foraged until dawn. In an artificial nest in 
room conditions they displayed striking dawn and dusk peaks of ac- 
tivity and of number out in the arena. In a darkroom in constant 
temperature and alternating light and dark, they were diurnal rather 
than crepuscular-nocturnal. In the same conditions a winged female 
in one counter assembly and a group of three males in another were 
each nocturnal, the males being especially active the first hour of 
darkness, and the female active at the first and last ends of the light 
period as well. Both male and female rhythms persisted in constant 
darkness, whereas worker rhythms did not perisist, at least in these 
brief experiments. The nature of the caste difference in rhythm 
deserves further study. 
Collection and culture observations are noted. Foragei'9 in the 
field return with droplets between their mandibles. Ants tested in 
the laboratory with sugar solution showed no mouth digestion of 
sucrose like that in the honeybee. 
Acknowledgements 
This work was done at the Biological Laboratories of Harvard 
University during the tenure of a postdoctoral fellowship (NSF 
49101) to ESM. It was supported also by a grant to WLB from 
the Milton Fund of Harvard University. Special thanks go to E. 
