1972 ] 
A l cock — Bembix americana 
16 
The fact that wasps were building i, 2 or 3 celled nests raised the 
question, could an individual female construct more than one type 
of nest or was each wasp rigidly programmed to make either 1 or 
2 or 3 celled nests? 
In order to answer this question, a group of 16 wasps were marked 
on the thorax with a dot or dots of acrylic-vinyl paint after they 
had brought a prey to a nest. Each was given a distinctive color 
combination. Twelve of those marked completed one or more nests 
from the time of marking (July 14-21, 1972) to August 5 when 
I left the Seattle area. 
Two wasps (E, H) that definitely made a single celled nest ini- 
tially built a multi-celled nest the second time. For 3 others (I, K, 
L) this is probably the case. One female (F) that made 2 single 
celled nests consecutively almost surely built a double celled nest 
the third time around. Only 1 wasp definitely built a second nest 
with fewer cells than the first one (C) . 
The pattern of building single celled nests first and multicelled 
nests later is supported by indirect evidence from the 1971 data. 
The first year, observations of americana were not begun until later 
in the season (July 24 as opposed to July 14 in 1972). Less than 
1/4 of the 1971 nests excavated were single-celled as opposed to 
3/4 of the initial nests in 1972. I strongly suspect that most of the 
burrows excavated in 1971 were the second or third nests of the 
wasps, whereas in 1972 I made an effort to mark an individual as 
soon as it was discovered at a nest. 
Discussion 
This study shows that the females in at least one population 
of B. americana are capable of building either single or multi-celled 
nests. It suggests moreover that females tend first to build 1 celled 
nests and that subsequent nests are likely to have more than 1 cell. 
Variation in cell number is not unknown in Bembix occurring 
in amoena, , belfragei , cinerea, and niponica (Evans 1966, p. 277, 
317, 352). This is only the second report of such variation for the 
abundant, widespread and well-studied americana suggesting that 
multi-celled nests are rare for this species. It is noteworthy that 
Parker’s description (1925) of the design of the 3 celled nests he 
studied in a population of B. a. comata matches mine to the ex- 
tent that the final cell tended to be located under the main burrow 
near the entrance of the nest. 
