HYMENOPTERA 



983 



the cell, facing outward, his little head just filling the opening. 

 Here he stands on guard for the greater part of the time until the 

 nest is provisioned and sealed up, occasionally varying the monotony 

 of his task by a short flight." "V\'e have frequently seen him drive 

 away the brilliant green Chrysis fly which is always waiting about 

 for a chance to enter an unguarded nest." "In one instance, with 

 nthrocinctum w^here the work of storing the nest had been delated by 

 rainy weather, we saw the male assisting by taking the spiders from 

 the female as she brought thein and packing them into the nest, 

 leaving her free to hunt for more." 



Some species of Trypoxylon are mud-daubers. Trypoxylon albi- 

 tarsis, a shiny black species with white tarsi, builds large nests of mud, 

 which consist of several parallel tubes, often three inches or more in 

 length, placed side by side. These nests are known as pipe-organ 

 nests. Each tube is divided by transverse partitions into several 

 cells, which are provisioned with spiders. The tubes when completed 

 are not covered with an extra layer of mud as is commonly the case in 

 the nests of other mud-daubers. When an adult is ready to emerge 

 from the cell in which it was developed, it mkes a hole through the 

 exposed side of the tube. 



For a monograph of Trypoxylon see Fox ('93). 



Subfamily SPHECIN^ 

 The Thread-waisted Wasps 

 These insects are termed the thread-waisted wasps on account of 



the great length of the petiole of the abdomen (Fig. 1199). With 

 these wasps the marginal cell of the fore wings 

 (2d R1+R2) is not appendiculate; the anal 

 lobe of the hind wings is large, extending to the 

 apex of cell M3+CU1+CU2 or beyond (Fig. 

 1200); and the middle tibise bear two apical 

 spurs. 



These are the most commonly observed of 

 all of our sphecoid wasps, as certain species 



build their mud nests in the attics of our houses; and, too, the 



^ 



Fig. iigg.Sceliphron 

 cementarium . 



Fig. 1200. 



-Wings of Sceliphron cementarium 



