158 HYMENOPTERA. 



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 Crabro singularis, according to the 

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

 requirements of their young. Other genera (Rhopalum pedicel- 

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

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

 readily excavate and refit for their habitations. The females 

 provision their nests with caterpillars, aphidoe, spiders, and 

 other insects. 



This family is most difficult to classif}' ; 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 bod}', as inferior to Blepharii^us, 

 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 genera 

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

 sculpturing and relative amount of pubescence or hirsuties ; in 

 the form and sculpturing of the x>i'opodeum (Newman), or tho- 

 racico-abdominal ring of Newport ; while the tip of the abdo- 

 men presents excellent generic and also specific characters, 

 depending 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 Pemphredoninse occur far north in abundance, 

 while Cerceris occurs farthest towards the tropics. 



The subfamilj'- PliilantMnm includes the three genera, Phi- 

 lanthus, Eucerceris, and Cerceris. In Philanthus (Fig. 84, wing), 

 the head is short, transversely suboval, the clypeus longer 

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

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

 mon form southward is Plulantlms vertilabris Sa}' (Fig. 85). 

 In Europe P. apivorus provisions its nest with hone^'-bees. 



