1970] 
Eberhard — W asps 
247 
indicate that A. humilis did not use cues from the orb to locate the 
spiders. Although these differences may be due to differences in the 
species, it seems more likely that Soyer misinterpreted some of the 
behavior he observed. 
Predatory behavior of Sceliphron caementarium 
Sceliphron caementarium is much larger than A. humilis (length 
about 25 mm vs. about 8 mm). This species has been recorded 
stocking its tubular mud cells with spiders in the families Araneidae, 
Thomisidae, Salticidae, Oxyopidae, Anyphaenidae, Clubionidae, 
Mimetidae, Theridiidae, and Lycosidae (Muma and Jeffers 1945). 
In general, they take spiders commonly found on plants (Rau 1935, 
Muma and Jeffers 1945). 
Two individuals of S. caementarium were observed searching for 
A. cornutus on and near the windows of the cottage, and 18 wasp- 
spider encounters were seen. S. caementarium appeared to use dif- 
ferent signals than those used by A. humilis to locate spiders. The 
wasps hovered near the windows, alighting occasionally and some- 
times walking across a pane or two, then flying on. They apparently 
oriented visually before landing since they almost always lit either 
on small dark spots which contrasted with their background (the 
white trim of the cottage) or in corners of window panes. Occa- 
sionally they lit on dark objects (usually masses of dead epheme- 
ropterans) suspended by spider threads. The contrast between a 
spot and its background appeared to be more important in deter- 
mining its attractiveness to a wasp than its shape, as the wasps often 
landed on dark spots bearing little resemblance to a spider crouching 
in its retreat. These wasps encountered only the spiders which were 
resting on the white woodwork of the house. 
There were A. cornutus orbs on and near the windows, and the 
wasps sometimes flew into them as they hunted, but the wasps were 
strong and heavy enough that they quickly freed themselves. Their 
hunting behavior was never noticeably altered by such an encounter, 
indicating that they do not use the presence of an orb as a cue signal- 
ling the presence of a spider. 
Memory of previous captures probably influenced the choice of a 
site for hunting: after depositing a spider in her nest (about 5 m 
away), one wasp resumed hunting at the same edge of the same 
window pane where that spider had just been captured. The intensity 
of hunting activities at a given site also may be influenced by previous 
experience at that site. Two windows which were examined only 
