THE PREDATORY BEHAVIOR OF TWO WASPS, 
AGENOIDEJJS HUMILIS (POMPILIDAE) AND 
SCELIPHRON CAEMENTARIUM (SPHECIDAE), 
ON THE ORB WEAVING SPIDER 
ARANEUS CORNUTUS (ARANEIDAE) 1 
By William Eberhard 2 
Museum of Comparative Zoology, Harvard University 
The nesting habits of many wasps have been studied, but much 
less is known of how they locate and capture their prey. Many 
wasps in the families Pompilidae and Sphecidae prey on orb weaving 
spiders, and knowledge of their predatory behavior is crucial to an 
understanding of the biology of orb weavers. This paper describes 
the hunting behavior of two species of wasp ? A genoideus humilis 
(Pompilidae) and the mud dauber Sceliphron caementarium 
(Sphecidae) which were observed preying on the orb weaver Araneus 
cornutus during July and August, 1968, and discusses the signifi- 
cance of their behavior for the spiders. 
There was a dense population of the spider Araneus cornutus on 
the windows and shingled walls of a cottage on Lincoln Pond in the 
Huyck Preserve, Rensselaerville, New York. Spiders spun orbs in 
the early evening and sat at the hubs during the night, then (except 
for a few younger individuals) left the orbs and crouched in retreats 
during the day. The retreats were usually approximately tubular, 
silk-lined, and often had silk just beyond the mouth. Although most 
of the retreats around the cottage were in cracks beneath shingles, 
the spiders were especially plentiful around windows from which 
lights showed at night, and there were a number of retreats at the 
edges of window panes (there were 15 30X15 cm panes/window) 
and in the corners of window frames. Retreats like these, which 
This is part of a thesis done under the direction of Dr. H. W. Levi 
and submitted to the Department of Biology of Harvard University, in 
partial fulfillment of requirements for the PhD degree. The work was 
done in 1968 while I held a Summer Fellowship from the E. N. Huyck 
Preserve, Inc.; I thank the directors and staff of the Preserve for making 
it possible for me to do this Work in such pleasant surroundings. I thank 
Dr. H. E. Evans for encouragement and for identifying the wasps, and 
Mary Jane Eberhard, Robert Jeanne, and William Shear for helpful com- 
ments on the manuscript. Specimens of the species observed are deposited 
in the Museum of Comparative Zoology, Cambridge, Mass. 
2 Present address: Depto. Biologia, Universidad del Valle, Cali, Colombia. 
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