24 
Psyche 
[March 
mon plant in primary forests of that region. Over 40 nests were 
collected during the course of this study; 27 of these were collected 
at night, when all adults were presumed to be inside. Up to 18 
cells and 10 females were found per nest, with many nests containing 
more than one female. 
THE STUDY AREA 
The study plot, approximately 44 meters square, was in a flat 
tract of undisturbed Tropical Rain Forest (terminology of Leopold, 
1959) south of Agua Buena Creek behind the Tropical Science Cen- 
ter Building, 3.5 miles southwest of Rincon, Osa Peninsula, Punta- 
renas Province, Costa Rica. The canopy, ranging from 35 to 60 
meters in height, was relatively closed. Understory plants were not 
particularly dense; it was possible to walk through the forest with 
relative ease. 
During the period of study (March 5-1 1 , 1967), relative humid- 
ity in the forest was above 80% both night and day and rain fell 
briefly nearly every day. The air temperature one meter above 
ground on a representative day ranged from 22°C at 0600 to 27-5°C 
at 1200. 
Fig. 1. Female of M'icrosUgmus comes Krombein. 
