968 AN INTRODUCTION TO ENTOMOLOGY 



honey. In this respect they differ from other solitary wasps in the 

 same way that the solitary bees differ from other sphecoid wasps. 

 But this difference in habits is not true of all masarid wasps as is 

 shown by the habits of the following species, which provisions its 

 nests with larvae. 



The only published account of the nest -building habits of an 

 American masarid is that by Dr. Anstruther Davidson ('13) who 

 described the nest of Pseudomdsaris vespoides. This is our largest 

 and most handsome species; it measures from 15 to 22 mm. in length, 

 is black marked with yellow, and is widely distributed in the Far 

 West; but is not common. Dr. Davidson's account of the nest 

 follows. 



Their nests, a combination of cells as shown in the accompanying illustration, 

 are built after the manner of the common mud dauber wasp and when completed 

 are plastered over with a further layer of clay. They are usually attached to a 

 twig in a low bush, the one in the illustration being found on a Audibertia shrub. 

 When the cell is completed the opening is closed by a stopper of clay which is, 

 however, always depressed below the rim of the cell so that the top shows as a 

 series of miniature cups. The clay used is that common to the neighborhood, 

 but in the process of building it is mixed with some secretion that makes the whole 

 of such stony hardness, that it seems impossible any insect could possibly cut its 

 way through it. Perhaps the cup shaped depression on top may be a device to 

 conserve the rain necessary to soften the stopper and render the exit of the wasp 

 possible. That rain or excessive moisture is necessary before the insect can 

 successfully emerge is suggested by the results attained in indoor hatching. 

 In those nests kept indoors in dry receptacles while the wasp usually attains the 

 mature state, it only exceptionally cuts its way out. Kept under these conditions 

 the larvae do not always matiu-e in the following spring as the following record 

 makes evident. Of a cluster of cells gathered in June, 1902; in April, 1903, I 

 opened two of them to find one had pupated while the other was still in the larval 

 state. It remained in this state till March, 1905, when it died. The other cells 

 were then opened, one contained a live larva, the other four or five contained 

 perfect insects all dead, apparently unable to emerge. The capability of insects to 

 survive for more than one season in the larval stage is probably an evolutionary 

 acquirement, and a necessity to those insects living on a food supply that is 

 wholly dependent on climatic conditions. As the writer has shown elsewhere in re- 

 cording a similar experience with Anthidium corisimile, this is a very necessary 

 acquirement in a country where, as sometimes happens, no rain at all may fall, 

 and no food supply would in those seasons be available. The cells are stored with 

 small larvae of what species I am unable to determine. 



As in the nests of the European species, the cells are lined with a 

 layer of silk. Figiu-e 1 184, a represents a nest given me by Professor 

 Doane of Stanford University; this is an incomplete nest in which 

 the cells have not been plastered over with an additional layer of 

 clay; Fig. 1184, b is a diagram of a longitudinal section of a single 

 cell showing the cup at the upper end; Figure 1184, c represents 

 a completed nest ; this was given me by Dr. Davidson. 



The subfamily ZETHIN.^^ is represented in our fauna by a single 

 genus Zethus. of which there are two species, Zethus spmipes and 

 Zethus slossoncB, common in the southeastern part of the United 

 States. 



Ashmead ('94) states that our Zethus spmipes builds globular cells 

 of clay or sand and mud mixed, which are attached by a small pedicel 



