1903 Fossorial Hymenoptera 27 



them from the Wasps and Ants. The true Wasps and 

 their allies (Diploptera) can be at once recognised by their 

 habit of folding their wings, when at rest, longitudinally, so 

 as to diminish their breadth by one-half, and prevent the 

 delicate hinder margin of the wing from overlapping the 

 dorsal surface of the abdomen. This leaves us only requiring 

 a character by which we may discern when we are dealing 

 with an Ant or one of its congeners (Heterogyna), and here 

 we find that the "waist" (petiole) affords a sure guide. In 

 the Fossores the petiole of the abdomen is simple, and, 

 moreover, the species are solitary, while in the Heterogyna 

 the petiole has on its dorsal surface at least one upstanding 

 scale, and the species are social, forming communities, which, 

 as a rule, consist of males, females, and workers. 



It is not improbable that a beginner might confuse some 

 of the Augur-bearing (Terebrantia) Hymenoptera, " Ichneu- 

 mon flies " in common parlance, with Fossores ; any of the 

 former may, however, be quickly "spotted" by the double 

 trochanter of the legs, and frequently by the long and curling 

 antennae. 



It is not my intention to give a detailed account of the 

 families and genera included within the limits of the 

 Fossores, but rather to speak of a few species with which 

 I am especially familiar. Of these I shall select one or two 

 from each of the two chief divisions which are structurally 

 distinguishable by the form of the dorsal part of the first 

 thoracic segment (pronotum). In the first division the pro- 

 notum is of great extent both dorsally and laterally, and its 

 angles reach back to the tegulse of the wings : this division 

 includes the Pompilidse and a few other less conspicuous 

 families. In the second division, known as the Sphegidas 

 or Sand-Wasps, the pronotum is not so produced, and often 

 is but a narrow collar. 



The Pompilidae are delightful little insects ; many of 

 them are brilliantly coloured with red and black markings, 

 and of fair size — about 1 inch long, though most are 

 smaller. They never make flights of any length, but prefer 

 running about in a bustling feverish sort of way, taking 

 short leaps and flights of a few feet at most. Nearly all of 

 them provision their nests, which are mere holes dug in the 



