38 PHIL RAU AND NELLIE RAU 



be recorded as an enemy of T. albitarsis, which frequently 

 causes heavy losses. It is a simple matter for a bird to peck 

 through the mud walls of the pipe-organ nests and on one occa- 

 sion a blue jay was actually seen breaking into the nest and 

 to feast upon the larvae therein. 



In addition to the above we have found one nest of T. albitarsis 

 infested by an Ichneumon fly belonging to the tribe Ophionini. 



In one collection of Sceliphron I found about a dozen cocoons 

 which, when held to the light, revealed an inner cocoon just 

 a little smaller than the mud-wasp's cocoon and of a lighter 

 color. I had found previously that the blue wasp makes an 

 outer webby cocoon over the papery one, but this seemed to 

 be a reversion of that arrangement. At emerging time there 

 issued from these Sphaerophthalma scaeva Blake, 13 a handsome 

 black Mutillid parasite with orange abdominal markings. This 

 species emerged from mud-daubers' nests collected in two differ- 

 ent localities and years. 



We find that the larvae of Sphaerophthalma scaeva Blake spin 

 their cocoons within the cocoons of Pelopoens. Since the nests 

 containing both were gathered in December and remained in 

 my living-room all winter, it was impossible for Sphaerophthalma 

 scava to parasitize the cocoons of Pelopoeus after they became 

 such, but in all probability the eggs of 5. scaeva remained dormant 

 until the Pelopoeus larva had finished feeding and spinning, 

 and then it developed, forming its own white cocoon within 

 the brown one of the Pelopoeus. Even this parasite we find 

 parasitized by Melittobia. 



Some old cells of T. albitarsis were infested by mites, prob- 

 ably Pediculodes ventricosus Newport, but since there was slight 

 mortality in this lot of material I presumed that the mites 

 had come after the emergence of the wasps to feed upon any 

 old spiders which chanced to be there. 



HOUSE-RENTERS 



These occupancies other than parasites may be called little 

 more than chance. But the empty cells of the three species 

 of mud-daubers here considered serve a very important function 

 in supplying permanent homes to at least four distinct species 



13 Identified by Mr. S. A. Rohwer. 



