158 HYMENOrTERA. 



of the species are wood-wasps, making their cells in cy- 

 lindrical holes in rotten wood, or enlarging nail-holes in 

 posts, as is the case with Grabro singularis, according to the 

 observations of Mr. C. A. Shurtleff, thus adapting them to the 

 requirements of their young. Other genera (Rhopalum pedicel- 

 latum, Stigmus fraternus, and Crabro stirpicola) avail tliem- 

 seivcs of those plants whose stem has a pith which they can 

 readily excavate and retit for their habitations. The females 

 provision their nests with caterpillars, aphidoe, spiders, and 

 other insects. 



This family is most difficult to classify ; it consists rather of 

 groups of genera, some higher and some lower, though as a 

 general rule those genera with pedunculate abdomens are the 

 lowest in the series. In illustration, we regard Stigmus, with 

 its elongated decephalized body, as inferior to Blepharipus, 

 which again is subordinate to the more cephalized Crabro, 

 where the body is shorter, the abdomen sessile, the anterior 

 part of the body more developed headwards, while its nests 

 are constructed more elaborately. The genus Psen, for the 

 same reason, is lower than Cerceris, of which it seems a de- 

 graded form. 



Some of the most useful characters in separating the genei'a 

 of this family are to be found in the form of the cl3q3eus, its 

 sculi)turing and relative amount of pubescence or hirsuties ; in 

 the form and sculpturing of the propodeum (Newman), or tho- 

 racico-abdominal ring of Newport ; while the ti[) of the abdo- 

 men presents excellent generic and also specific characters, 

 dei)ending on its grooved or flattened shape. 



The species of this family are mostly found in the north 

 temperate zone, being very abundant in North America and in 

 Europe. The Pemphredoniuje occur far north in abundance, 

 while Cerceris occnrs farthest towards the tropics. 



The subfamily Philanthiure includes the three genera, Phi- 

 kmtliHS, Eacerceris, and Cerceris. In Philantlius (Fig. 84, wing), 

 the head is short, transversely suboval, the clypeus longer 

 than broad, with the first joint of the abdomen nearly as broad 

 when seen from above as the succeeding one. Our more com- 

 mon form southward is PlnJanthus rerfilahn's Say (Fig. 85). 

 In Europe P. upivorus provisions its nest with hone3'-bees. 



