1970] 
Eberhard — • JV asps 
249 
Twice a wasp captured and then discarded a very small spider. 
Both spiders, which were less than half the size of the wasp’s head, 
were captured at the bottoms of their retreats, stung in midair, then 
dropped as the wasp resumed hunting. There were a number of 
individuals of A. cornutus on the windows where the wasps hunted 
which were too large (i.e. larger in diameter than the wasp’s mud 
cell), but no encounters with these individuals were observed. Some- 
times the wasps appeared to avoid their retreats. 
Occasionally hunting wasps paused and flattened themselves on a 
flat, light-colored surface in the sunlight. These pauses probably 
functioned to elevate the wasp’s body temperature. The predomi- 
nantly black coloration of S. caementarium (and A. humilis ) may 
function to speed this process, but this is not certain since many 
wasps which do not obviously need to collect heat are also black. 
Wasps attempted to sting three different empty spider skins which 
hung near empty retreats. Thus the stinging behavior of S. caemen- 
tarium is probably released by the stimuli of contact with the surface 
of the spider, just as it is in A. humilis. This response would, be 
highly adaptive for both wasps when they hunt for spiders which are 
difficult to see after they drop into litter below the retreat and assume 
cryptic postures. Apparently contact with arthropod cuticle of all 
kinds will not release stinging; once a S. caementarium landed on a 
phalangid (daddy-long-legs), but immediately flew on; the phalangid 
remained motionless. 
The wasps did not capture all spiders they encountered. Twice a 
wasp failed to react when a spider fell from the retreat she was 
tearing at. Another relatively small spider was blown some distance 
as it descended on a thread, and the wasp did not follow it. Two 
other times, a spider did not leave when a wasp pulled at its retreat, 
and after several tugs the wasp moved on. Both of these retreats 
were exceptional. One was under a large mass of dead ephemer- 
opterans and spider silk and the wasp pulled at this mass rather than 
the retreat. The wall of the other was unusually strong because it 
was quite thick and made of thick fibers spun by a relatively large 
spider. 
The observations above are not in complete agreement with pub- 
lished observations of S. caementarium predatory behavior. The 
Peckhams (1905) also saw this species ( — P'elopaeus caementarium ) 
hunting Araneus cornutus ( = Epeira strix) on the side of a house, 
but recorded that the wasps walked along the wall and pried into 
nooks and crannies rather than hovering nearby and landing on dark 
