280 
Psyche 
[Vol. 89 
(details in Lawton and Dryer, 1980). Frequent rains deposit approxi- 
mately 3000 mm of precipitation annually on this area. Heavy mists 
augment this precipitation. Mean annual temperature is about 16°C 
(max = 27° C, min = 10°C) and during prolonged rainstorms, the 
temperature can remain at 15— 16°C for 3-4 days. The wind generally 
blows 15 to 20 km/ hr, but ranges from nearly calm to winds in excess 
of 100 km/ hr during rainstorms (R. Lawton, pers. comm.). 
Nesting aggregation No. 1 was directly on the Continental Divide, 
on a narrow ridge known as “La Ventana”. The aggregation was first 
noticed in August 1975 and was still active but reduced in size to only 
5 nests in February 1981. W. Guindon (pers. comm.) indicated the 
site was active as early as 1966. Bees apparently maintained nests in 
this area throughout the year (R. Lawton, pers. comm.). Nests were 
built in the lee of a slope which partially protected them from mist 
and rain (Fig. 1). In July 1977, there were 97 nests with tumuli in the 
approximately 18 m aggregation. The majority of the nests were 
within an elliptical area of about 8 m. Of the nests 29 were completely 
exposed in the trail, 50 were on nearly level ground and partially 
obscured by grasses and other herbs, and 18 were on the face of the 
sheltering embankment. 
Nesting aggregation No. 2, located at the head of the valley on the 
road to Penas Bancas, was exposed to high winds and unprotected 
from rain (Fig. 2). In February 1978, the aggregation consisted of 
not more than 100—150 nests, but had enlarged to at least four 
hundred active nests by August 1978. Nests were found both on the 
edge of the road and down the adjacent steep, bare slope. By the last 
visit to the site in February 1981, the number of active nests had 
declined to 230. The adjacent slope had become covered with dense 
vegetation and lacked nests. 
Description of the Nest 
Entrances to active nests had tumuli approximately 7.5 cm in 
diameter and 4-7 cm in height (Fig. 3). The frequent rains obliter- 
ated tumuli of all nests except those in which bees were actively 
digging. Nest entrances consistently measured 1.0 cm in diameter. 
In each of three nests excavated in horizontal ground, the tunnel 
began nearly vertically for 7—14 cm and then continued downward 
at an angle of approximately 75°. In the diagrammed nest (Fig. 4) 
