A NOTE ON THE PREY AND A NESTING SITE OF 
CERCERIS TRUNCATA CAMERON (HYMENOPTERA: 
SPHECIDAE: PHILANTHINAE) 
By F. G. Werner 
Department of Entomology, University of Arizona 
This species seems to be very rare or extremely local in southern 
Arizona; Dr. H. A. Scullen, who has kindly provided the identifica- 
tion, held it as undescribed until he discovered that it had been 
described from Mexico by Cameron. However, there is a rather 
extensive nesting site in my own yard, at 1247 N. Warren Ave., 
Tucson. During the past four years I have been able to observe the 
habits of the species regularly and have found that the females store 
only beetles of the family Bruchidae ( Mylabridae) . The species 
stored at this site are all of medium size, and probably all come from 
leguminous trees and shrubs in the neighborhood. In order of abun- 
dance the bruchids gathered are: Algarobius prosopis (Lee.), Ali/no- 
sestes protractus (Horn) , Mimosestes amicus (Horn) and N eltumius 
arizonensis (Schffr.) ; this is roughly the relative abundance of these 
species when they are taken in general collecting. The most abundant 
source tree in the neighborhood is the so-called Mexican palo verde, 
Parkinsonia, which is planted extensively, blooms in the spring and 
has mature pods by mid-July, when the wasps become active. 
The site occupied is on fiat ground in the southwestern corner of 
the lot, about 10' x 10', shielded on south and west by a five-foot wall 
and partly shaded by large oleander bushes ; the soil is bare and con- 
sists of well-packed fill about eight inches deep over caliche ; almost 
all of the water that reaches it comes from rainfall. Activity of the 
wasps was checked weekly in 1958, when the first swarms of males 
and starts of nests were observed on July 20 and could not have started 
more than a week before this date. The males fiy continually during 
the day, just over the oleander bushes and nearby vegetation, stopping 
occasionally to rest. Hundreds of individuals are involved in these 
flights. Smaller numbers, usually about twenty, patrol the nesting 
site, flying about four inches above the ground, and attempt copulation 
with females flying in the area or returning to their nests with prey. 
I could not discover where the males went at night. The females dig 
small holes, either bare or with a low mound up to ij/2" in diameter. 
Most of their flying and provisioning activity occurs in the morning 
but even then the principal activity seems to consist of sitting in the 
nest entrance with only the front of the head exposed. By noon all 
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