Parasites and Predators 



account. Still within the head of its victim the fly grub 

 changes into a chrysalis. 



All the parasites we have described are external ; they 

 live outside the bodies of their hosts. There are also a 

 very large number of insect parasites which never see the 

 light of day during their immature stages, dwelling all 

 the while within the body, which at once provides them 

 with board and lodging. A very remarkable fact about 

 these internal parasites is that, though they may live and 

 feed for a considerable period within the body of some 

 luckless caterpillar, for instance, they never touch any 

 vital organ till their feeding days are over and they are 

 ready to change into chrysalids. By avoiding the vitals 

 they ensure a supply of food for themselves as long as it is 

 needed. 



Before leaving the insect parasites let us notice two 

 points. It is an almost universal rule in the animal 

 kingdom that a single egg produces a single young one. 

 A search amongst parasitic insects will reveal exceptions 

 to this rule. There is a little parasite given to laying its 

 eggs in those of a moth closely related to our clothes- 

 moth. Each parasite egg gives rise to several grubs which 

 feed upon the bodies of their host larvae. We all know the 

 old saying concerning big fleas having little fleas, etc., but 

 few of us realise how true in fact these words are. They 

 are well exemplified in the many cases of hyperparasitism 

 that is to say, cases where a parasite is itself preyed 

 upon by another parasite ; and this reminds us of a triple 

 tragedy which actually took place. 



During the gipsy-moth's depredations in America it 

 and its doings were very carefully studied with a view to 

 discovering certain parasites which might lend their aid 

 in getting rid of the moth. During some investigations on 

 the eggs of the moth a certain insect was found to deposit 

 its eggs therein. Hardly were the parasite's eggs safely 

 packed away within those of the gipsy-moth when another 

 insect a hyperparasite came along and deposited a 



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