Vol. 67 
No. 3 
PSYCHE 
September, i960 
A STUDY OF BEMBIX U-SCRIPTA , 
A CREPUSCULAR DIGGER WASP 
By Howard E. Evans 
Museum of Comparative Zoology 
One of the most characteristic features of the digger wasp genus 
Bembix is the almost complete obliteration of the ocelli. Two North 
American species, arcuata and u-scripta, provide the only important 
exceptions to this, and these species also possess several other structural 
features which set them aside from all other species of Bembix. A 
few years ago I presented some very incomplete data on a colony of 
u-scripta in southern Texas, suggesting at the same time that the be- 
havior of the species ought to prove of unusual interest because of 
its apparently primitive structural features (Evans 1957)- I have 
recently made further studies of this same colony and also of another 
small colony in southwestern New Mexico, thus providing an unusual 
opportunity to compare the behavior of two widely separate colonies 
of an uncommon species of distinctly localized distribution. 1 hese 
studies also demonstrate that u-scripta has one very remarkable feature 
in its behavior: the females hunt and provision only in the dusk, 
around and after sunset. Throughout the higher Hymenoptera, large 
ocelli are distinctly correlated with nocturnal flight. It seems very 
probable that the preservation of functional ocelli in this species repre- 
sents an adaptation for flying in the twilight. 
A second problem concerns the identity of Bembix arcuata : is this 
in fact a distinct species from u-scripta ? The Texas colony was located 
not too far from the type locality of arcuata, the New Mexico colony 
not far from that of u-scripta. The New Mexico wasps had a much 
more extensively yellow color pattern (more like u-scripta) , but there 
was considerable color variation in wasps from both localities. In 
fact, on the basis of the Texas locality alone, I have already tenta- 
tively placed arcuata in the synonymy of u-scripta (Evans 1959 )- 
Clearly it will be of interest to see what light behavior sheds on this 
matter. 
In this paper I shall first consider the structural peculiarities of 
Bembix u-scripta and also the differences which are supposed to sepa- 
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^THSONIAN 
■^BTHTOTION 
