SPHEGIDAE CRABRONIDES 



129 



variable in form, pedicellate in some abnormal forms, but more 

 usually not stalked. 



The Crabronides ( Vespa crabro, the hornet, is not of this sub- 

 family) are wasp-like little Insects, with unusually robust and 

 quadrangular head. They frequently have the hind tibiae more 

 or less thickened, and the clypeus covered with metallic hair. 

 It appears at present 

 that they are specially 

 attached to the tem- 

 perate regions of the 

 northern hemisphere, 

 but this may possibly be 

 in part due to their 

 having escaped attention 

 elsewhere. In Britain 

 they form the most im- 

 portant part of the 

 fossorial Hymenoptera, 

 the genus Crabro 

 (with numerous sub- 

 genera) itself comprising thirty species. The males of some of 

 the forms have the front tibiae and tarsi of most extraordinary 

 shapes. They form burrows in dead wood, or in pithy stems, 

 (occasionally in the earth of cliffs), and usually store them with 

 Diptera as food for the larvae : the wings and dried portions of 

 the bodies of the flies consumed by Crabronides are often exposed 

 to view when portions of old wood are broken from trees. 



The genus Oxybelus is included by some systematists, but 

 with doubt, in this sub-family ; if not placed here, it must form a 

 distinct sub-family. It has the metathorax spinose, and the sub- 

 marginal and first discoidal cells are not, or are scarcely, separated. 



Crabro leucostomus has been observed by Fletcher to form 

 cells for its larvae in the soft wood of broken willows : the food 

 stored therein consists of two-winged flies of the family Dolicho- 

 podidae. This Crabro is parasitised by an Ichneumonid of the 

 genus Tryphon, and by a two-winged fly of uncertain genus, but 

 belonging to the family Tachinidae. The metamorphoses of 

 Crabro chrysostomus have been briefly described by Verhoeff: 

 the food stored consists of Diptera, usually of the family Syr- 



VOL. VI K 



FIG. 52. Crabro cephalotes ?'. Britain. 



