1968] 
Matthews — - Microstigmus 
25 
Eighty-eight Crysophila guagara Allen plants were found in the 
study area. Figure 2 is a map of their distribution and the distribu- 
tion of wasp nests in the study area. These plants ranged from 
seedlings to mature trees approximately 40 feet tall, but nearly half 
of the plants in the plot were 5 feet or less in height. The number 
of fronds per plant ranged from 4 on the smallest seedlings to a 
maximum of 22 on some of the mature trees. 
Seventy-four wasp nests from 38 plants were counted in the plot ; 
this was probably less than the total number of nests present, as 
it was difficult to see nests in the tallest trees. Nests were most easily 
seen after dark, when they stood out plainly in a flashlight beam 
against the white undersides of the leaves. 
Figure 3 shows the distribution of nests as related to plant size 
class. Trees of 20 feet or less in height were the preferred nest sites, 
with the greatest number of nests occurring on trees between 6 and 
10 feet tall. Sixteen plants had one nest only; 14 had 2 nests; 7 
had 3 nests; one had 4 nests and one had 5 nests. This appears to 
be a high density for a primary forest predaceous insect, but may be 
a result of the ease of finding nests. By contrast, 800 sweeps with 
a net in similar vegetation in an adjacent area yielded only one 
adult of this wasp. While there appeared to be plenty of suitable 
nest sites available, Figs. 2 and 3 indicate certain sites were pre- 
ferred. This fact may be significant in the evolution of social 
behavior in this species since a clumped nest distribution is likely to 
increase the probability of nest-mates being relatives (see Hamilton, 
1964). 
The nest (Fig. 4) is suspended from near the midrib of the leaf, 
usually about half the distance to the tip, and approximately at the 
point where the leaf curvature is greatest. Occasionally there were 
two active nests on a single leaflet, and once three were found. The 
broad leaf protects the nest from the rain that would almost certainly 
destroy an exposed nest. Nests were always on the younger fronds. 
Older fronds having a large amount of epiphilous algal growth had 
no active nests although they often showed evidence of having once 
had them. According to D. H. Janzen (pers. comm.), leaves begin 
to acquire epiphilous growth at about 5 months of age, suggesting 
that the life of a wasp nest is less than six months. Indeed, T. C. 
Emmel (in litt., 22 Aug. 1967) states that he could find no nests 
in the same locality during August 1967, despite extensive searching. 
NEST STRUCTURE AND CONTENTS 
Nests are constructed entirely from the waxy bloom coating the 
