128 



HYMENOPTERA 



CHAP. 



information exists as to their habits ; but Yerhoeff states that 



the species of Psen like mem- 

 bers of the Pemphredoninae 

 do not form cocoons. 



The Pemphredonine subdivi- 

 sion includes numerous small and 

 obscure Insects found chiefly in 

 Europe and North America (Fig. 

 51, P. lugulns}; they resemble 

 the smaller black species of Cra- 

 bronides, and are distinguished 

 from them chiefly by the exist- 

 ence of at least two complete, 

 FiG.50.-mmesaUcolori. submarginal cells on the an- 



Bntam. 



terior wing instead of one. 



The species of Passaloecus live in the burrows that they form 

 in the stems of plants ; Pemphredon lugubris frequents the decayed 

 wood of the beech. The larva and pupa of the latter have been 

 described by Verhoeff; no 

 cocoon is formed for the 

 metamorphosis. Both these 

 genera provision their nests 

 with Aphidae. This is 

 also the case with Stigmus 

 pendidus, but the burrows 

 of this species form a com- 

 plex system of diverticula 

 proceeding from an irregu- 

 lar main channel formed in 

 the pithy stems of bushes. 

 Cemonus unicolor, according to Giraud, forms its burrows in 

 bramble -stems, but it also takes advantage, for the purposes 

 of nidification, of the abandoned galls of Cynips, and also of 

 a peculiar swelling formed by a fly Lipara lucens on the 

 common reed., Arundo phragmites. This species also makes 

 use of Aphidae, and Verhoeff states that it has only an imperfect 

 instinct as to the amount of food it stores. 



FIG. 51. Pemphredon Iwjubris 9- Britain. 



Sub-Fam. 10. Crabronides .--Pronolum short, front winy /'//// 

 one complete submarginal and two discoidcd cells: hind body 



