CH. V] WASPS 155 



Wasps are, however, very useful both as scavengers and 

 as destroyers of insect pests. The dead bodies of small 

 mammals, such as mice, are in a few days stript of all flesh 

 by their powerful jaws and rendered inoffensive. I once 

 witnessed a wasp swoop upon a large garden spider that 

 was sitting in the centre of its web and carry it off without 

 in any way disturbing the silken cords of the web. Earwigs, 

 blue-bottle flies and other Diptera, Aphides (greenfly and 

 blackfly), small caterpillars and many other insects are 

 captured by them and carried off to feed their larvae in 

 their combs. It is thus evident that though at times 

 wasps do injury in orchards arid gardens, yet they are of 

 considerable service to us in reducing the number of 

 injurious insects. 



Parasites. A large number of parasites have been 

 observed in and about the nests of wasps. It is doubtful 

 if the majority of these are really to be regarded as true 

 parasites. More probably they play rather the part of 

 scavengers and are therefore in commensal association 

 with their hosts. The wasps themselves are scrupulously 

 clean in their habits. They always proceed to the entrance 

 at the lowest part of the nest to void their excreta. Hang- 

 ing on to the edge of the envelopes of the nest they 

 extend the abdomen vertically downwards and discharge 

 their evacuations upon the ground below. Hence beneath 

 the nest there is a considerable accumulation of organic 

 matter. In the soil beneath the nest are usually numerous 

 larvse of Pegomyia (Acanthiptera) inanis. These Dipterous 

 grubs appear to feed upon the debris of food and excre- 

 ment that proceed from the nest. Their eggs are laid by 



