284 
Psyche 
[Vol. 89 
that these bees had spent the night away from their nests as occurs 
with Bombus species at high elevations (O. R. Tayor, pers. comm.). 
Before leaving the nest for the first time in the morning, females 
often remained just below the nest entrance for a few moments and 
then upon exiting, hovered nearby for a short time before flying off. 
Temperatures within the nest entrance remained at 12°C through- 
out the day on February 20 when ambient temperature was between 
10-1 1°C. 
Males remained outside the nests at all times. During the activity 
period of the females, the males flew over the nesting aggregation 
and nearby at heights of 1-3 m. They rapidly approached any flying 
object, including female C. luctuosa, swallows, a hummingbird, a 
ctenuchid moth and a dragonfly. Males often seized females return- 
ing to the nests but it was not ascertained whether copulations 
occurred. 
Nest Visitation Behavior 
On February 19 and 20, 1978, 46 nests within a 2. 16 m subarea of 
aggregation No. 2 were mapped and numbered. Sixteen female bees 
were captured while leaving nests. Each bee and her corresponding 
nest of origin were given an identifying color combination. The bees 
were marked by paint spots on the thorax, while their nests of origin 
were indicated by a wooden chip about 1 cm in length placed near 
the entrance. All observed departures from and arrivals to mapped 
nests were recorded by noting time, markings (or lack thereof) of 
bees and nest number or color. A nest “visit” was defined as the 
disappearance of the bee beneath the ground surface for any length 
of time. 
Of the 46 nests mapped, 40 (80%) were entered at least once by a 
bee. The number of observed visits per nest made by marked or 
unmarked bees to the 16 color-coded nests ranged from 0-15 over 
the two days (Table 1). 
Of the 16 marked bees, four were not observed again. The remain- 
ing 12 marked bees visited nests a total of 78 times. Four of the 
marked bees (BG, GO, YBY, OB) concentrated their visits on a 
single nest, while others entered up to 12 different nests over the two 
days (Table 2). 
The duration of visits of both marked and unmarked bees varied 
widely from less than 1 minute to a maximum of 151 minutes. The 
