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[Vol. 92 
parasitism (10 of 39). When all of the nests constructed by females in 
which a prey was placed (~ used nests; see Hager and Kurczewski, 
1986) are considered, S. vigilans successfully parasitized 1 .63% (4 of 
245) of the nests, while another 2.45% (6 of 245) of the nests were 
presumed parasitized, making a total of 4.08% (10 of 245) parasit- 
ized used nests. 
Of eight A. harti cells containing S. vigilans maggots, three each 
also contained a wasp larva, four had prey only, and one cell con- 
tained two maggots and prey. From the nests with prey only, two 
flies emerged the following June and three others failed to emerge. 
In the cells also containing a wasp larva, the maggots disappeared 
within a day. Either the wasp larva consumed the maggot(s) or it 
outcompeted the maggot(s), resulting in its(their) starvation. One 
wasp larva actively moved from a fresh prey on which it was feeding 
to a prey that was parasitized. Three hr later, the maggot could not 
be found. 
Counter-cleptoparasitic behavior 
A provisioning wasp responded to the presence of an S. vigilans 
by either “freezing” on the sand for up to 10 min (x = 4.3 ± 3.6 min, 
N = 9), flying to surrounding vegetation for up to 15 min (x = 6.6 ± 
5.2 min, N = 13), or alternating periods of “freezing” with low 
hopping flights near her nest. A. harti sometimes turned and faced 
S. vigilans before freezing. At other times, the wasp would fly at the 
trailing flies. Success of “freezing” depended upon the number of 
flies present and the number of active wasps in the vicinity. In 
periods of high nesting density and activity, flies were easily dis- 
tracted by the movements of other wasps and “freezing” was effec- 
tive. Flights to vegetation were successful for the same reason. 
Prey abandonment was observed once under continuous pressure 
from five trailing S. vigilans. Unsuccessful in evading the flies (sev- 
eral landed on the prey), the wasp crawled up vegetation and aban- 
doned her prey. She proceeded to her nest, opened it, searched for 
her prey, but never relocated it. Six S. vigilans and a hyperparasite, 
Perilampus hvalinus Say (Perilampidae), were reared from this prey 
(see Spofford and Kurczewski, 1984). 
Another response by A. harti to the presence of S. vigilans was 
nest cleaning (see Hager and Kurczewski, 1986). The number of 
times a wasp entered and removed sand from her burrow was a 
function of her activity (inspecting or provisioning) and the absence 
