1979] O’Neill — Behavior of Philanthus psyche 
29 
y the territorial males. It is evident that the pursuit response as 
measured above was investigative rather than aggressive The 
response becomes aggressive only if a pursued male reacts and a 
swirling flight ensues. 
, ^ "j s P onse t0 females with P re y is less than that to males 
(P — 0.016; t-test) and females without prey. The proximate cause 
for this may be that the female with prey flies slower and is bulkier 
in appearance because of the burden she carries. An ultimate cause 
may n m u fCmaleS With Prey are not sexuall y receptive, having 
in all likelihood mated prior to or early in the sequence of nest 
provisioning. 
Species that differ greatly in appearance and habits from female 
. psyche, such as male velvet ants, spider wasps, asilid flies, 
butterflies and Ammophila spp. were merely approached or chased a 
snort distance (never more than 70 cm; N = 110). In contrast 
Bembecinus nanus, a sphecid wasp similar in appearance and habits 
to nonspecific females, drew nearly the same response as females 
with prey (t-test, difference not significant). Coloration seems to be 
an important characteristic, but not the only one to which the males 
C m' ,^ 1S J S 6Vldent b£CaUSe the bomb y Iiid % and the cuckoo wasp 
which differ greatly in appearance from the females, usually (twenty- 
eight of thirty-four cases combined) drew more than a simple 
approach response from the males. The response to these two was 
sigmficantly different (p < 0.05) than that given to Bembixpruinosa 
( . pallidipicta ) a sphecid with color patterns similar to P psvche 
but of differing flight characteristics. Evidently, flight characteristics 
(speed and/or flight pattern) of the intruder are involved in 
motivating the male. 
Predation Upon Males 
One possible constraint upon the evolution of a mating system is 
the susceptibility to predation which a particular strategy imposes 
upon the males. There is a perceivable risk of predation by visually 
hunting robberflies (Asilidae) caused by the exposure of males 
during the large number of flights they take while on the territories. 
The rusk is particularly high when these flights are directed towards 
robberflies intruding on the territory. Robberflies constituted al¬ 
most 5% of the intruders that the males approached and/or pursued 
while territorial. Four attempted predations were observed two of 
these successful. Predation will be discussed in more detail in 
another paper (Gwynne and O’Neill in press). 
