128 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



and active Wasp Fly (fig. 21), and soon meets its partner, and 

 again another batch of eggs is laid where Green Flies most do 

 congregate. I consider it the bounden duty of every gardener 

 to become acquainted with the Wasp Flies in all their changes, 

 and to conscientiously avoid killing them. 



Some of the Green Flies may even contain " blessings " in the 



shape of minute 

 parasitic Flies. 

 One of these is 

 shown at fig. 22. 

 A little experience 

 and patience will 

 soon enable any- 

 one to detect these 

 very fat Flies, 

 which generally 

 lose their green 

 colour, and attach 

 themselves some- 

 what apart from 

 their fellows, and 

 gradually become 

 of a dry appear- 

 ance and brown 

 or white in colour. 

 From each of 

 these emerge 

 small four-winged 

 Flies of different 

 species, the most 

 plentiful (Aphi- 

 dius) being shown 



at fig. 22. These and other allied species are in the habit 

 of running about the green Flies, tapping them on the back 

 with their long antennae and sounding them to ascertain if 

 they already contain a parasitic grub ; if not a rapid leap is taken 

 upon the back of one, and nolens volens a hole bored through 

 the skin and an egg of the parasite deposited in the stomach cf 

 the Green Fly. This egg soon hatches to a maggot which feeds 

 upon the juices contained, and of course in due time destroys 



V 



Fig. 20. 



