148 
Psyche 
[September 
the true nest entrances. Shappirio (1948) observed this same species 
of mutillid entering nests of P. gibbosus at Washington, D. C. It 
seems very probable that this species is a parasite of several species 
of Philanthus, although no one has actually reared it from cells of 
these wasps. 
Discussion. — False burrows are a characteristic feature of the 
nests of several nyssonine digger wasps (e.g., Tsuneki, 1943, Evans, 
195 7) and of at least one sphecine wasp (Tsuneki, 1963). There 
are now many observations of mutillid wasps and miltogrammine flies 
being attracted to these burrows, and bombyliid flies have been 
observed ovipositing in false burrows of certain species. There is no 
evidence whatever that these burrows play a role in orientation, rest- 
ing, or storage of prey. Tsuneki and I are in agreement that their 
function must be to divert parasites, and in a paper in preparation 
I shall attempt to trace their evolution, in the Nyssoninae, from 
quarries used for soil for closure to ritualized false burrows serving 
a very different function. The occurrence of false burrows in the 
Philanthinae has not, to my knowledge, been recorded previously. 
They were found to occur in all nests in both areas of study, but 
they may not occur in all individuals throughout the range of this 
species (geographic variation in this feature was found to occur in 
Bembix pruinosa by Evans, 1957, and has since been found in certain 
other species). It is important that this behavior be recorded in all 
species in which it occurs, and in various localities. 
In the case of P. lepidus , the false burrows would seem to afford 
no protection against Senotainia , which appeared to be the major 
enemies in both areas of study. Presumably the selection pressure was 
provided at a time and place when hole-searching miltogrammines, 
bombyliids, chrysidids, and mutillids were of major importance. 
Otherwise the behavior of P. lepidus does not differ in any major 
way from that of gibbosus and bilunatus, which make similar nests, 
maintain an outer closure, and do not level the mound at the nest 
entrance. P. lepidus nests later in the season than those species, 
emerging slightly later even than solivagus. The latter is a larger 
species which preys mostly on larger bees, sometimes on wasps; in 
the area of study solivagus nested in a slightly different situation, 
although there was some intermingling of nests. That the five species 
of Philanthus common in the northeastern states have been only 
partially successful in “dividing up the sand + bee niche” probably 
means, as suggested earlier, that the populations of all five are kept 
fairly low by parasite pressure. All five have developed certain 
behavioral mechanisms apparently serving to reduce the incidence 
