Parasitic Insects 



chrysalides therein, to emerge in due course and 

 parasitise other white butterflies. These masses of 

 cocoons are often destroyed in ignorance. They 

 should be preserved. 



But for natural checks to their increase, we might 

 look to these parasites to do all necessary for the 

 control of pests. Unfortunately in the artificial 

 conditions of o\ir gardens their work is not entirely 

 successful ; this partly because parasitised cater- 

 pillars become sluggish and f aU easy victims to birds, 

 and the parasites are themselves often destroyed by 

 parasites. 



Not only are caterpillars liable to be parasitised, 

 but all other pests. The brown skins, somewhat 

 distended, of greenflies are by no means infrequent 

 on the underside of the foliage they frequent. Close 

 examination reveals a minute hole in the skin, show- 

 ing where the parasite has emerged and left the 

 skin otherwise intact. Others stiU remain intact, 

 the parasites in them. Other insects may similarly 

 be attacked, while sometimes fungi are parasitic 

 upon pests and bacterial or fungus diseases attack 

 them. The caterpillar of the garden swift moth, for 

 instance, is often foimd in a " mummy " condition, 

 with the fruit of the fungus which has invaded all 

 the tissues of the caterpillar and formed the mummy 

 projecting from its body. 



Another parasite of insects frequently attracts 

 attention since it is found on leaves, especially in 



140 



