162 Aphides and Savwflies [CH. 
On a plant attacked by aphis may be found among 
the living forms a number of inflated skins of a whitish 
colour looking like small balls. These are the dead 
lice which have been killed by ichneumon wasps. 
These little wasps lay their eggs in the bodies of the 
lice and as the louse grows its parasite also grows and 
kills it. From the inflated skins the ichneumon wasps 
hatch out and continue their useful work of keeping 
down the number of aphides by laying their eggs in 
them. 
Fig. 50. Lace-wing fly. Eggs. Two larvae, one with the skins of its 
victims on its back and one adult. 
Earwigs eat large numbers of green flies and also 
their eggs. 
Considerable damage is done by aphides in hot dry 
weather. Rainy weather is unfavourable to their de- 
velopment. 
Remedial Measures. 
It must be borne in mind that a certain number of 
green flies are killed by other insects. The best means 
of keeping down these pests is to spray with some 
solution containing soft soap as a basis. The soft soap 
