[Vol. 94 
248 Psyche 
Fig. 2. LD arena rhythm of group of workers from BCI colony. Ants out in 
arena, mean ± SE, days as replicates (one-way ANOVA), Mar. 10-14. E. tubercula- 
tum, P< .001; E. ruidum, P = .01. 
again. Counts were started at 0600 Feb 15. They rose toward the 
highest near light-off of what had been the single night light expo- 
sure (2000-0800 in Fig. 3). The hourly pattern is consistent from day 
to day (ANOVA P < .001). [Still assuming a 24-h free-running 
period, the peak in Fig. 3 appears somewhat early: the peak hour of 
a cosine-fitted (P < .001) curve was about 0500, instead of 0800 (i.e., 
the new ‘dusk’ hour) as expected if the rhythm had been completely 
inverted.] 
(In DD Mar. 15-18, the pattern was much less clear, and neither 
it nor records later in March- April are shown.) 
Discussion 
What do these observations say about rhythmic behavior in E. 
tuberculatum ? 1) The colony was notably rhythmic in the field, the 
ants appearing outside the nest primarily at night. 2) A colony 
fragment in lab constant temperature exhibited a similar rhythm, 
indicating that it is not simply a reflection of cyclic field tempera- 
ture. 3) In constant darkness there was evidence for persistence of 
rhythm, indicating that it is not simply a response to the light-dark 
cycle of the field, either. 
