68 SOME SOUTH INDIAN INSECTS. ETC. [CHAP. VIII. 



account should such caterpillars require to be controlled as 



A parasite is an organism which lives al the expense and to the 

 detriment of another organism, and this latter we call its host. 

 Fleas, Itch-mites, Lice and Bed-bugs arc familiar examples and 

 >onn- species of each class all have man as their common host. 

 These are Ectoparasites or external parasites, living outside the 

 > the host, but many forms are Endoparasites living inside 

 the body of the host, and as examples of the latter class we maj 

 cite the malarial parasite, the plague bacillus, and intestinal worms. 

 Probably no ire exempt from the attacks of parasites, 



whether these be other insects or other animals (worms, protozoa, 

 eti .) or plain- (fungi and bacteria). The parasite-, themselves are 

 often attacked by other parasite's, which we call Hyperparasites, 

 and these again may be parasitized bj yet others. Truly the poet 

 wrought better than he knew in writing: — 



l)is< (leas have little fleas 

 I 'pun theii bai em, 



And little fleas have lesser fleas 

 And sii ad mfinitum. 



An original parasitic attack upon a hosl is called Primary Para- 

 sitism, the term Secondary Parasitism being applied to all subse- 

 quent attacks bj parasites. Hyperparasitism is the normal attack 

 pecies oi p irasite upon another species of parasite and 

 superparasitism occurs when a normally primary parasite attaeks 

 a host already parasitized, the result generally being (in the case 

 of insects and their usual endoparasites) that the tissues of the 

 hosl prove insufficient to meet the needs of the latest comer so that 



it is forced to attack its predecessors. 



The foregoing paragraph technical, but it is none the 



less of the verj first importance to obtain a very clear idea of the 

 final result ol parasitii attack. Insects which become pests of 

 i rops frequently increase to destructive numbers because parasitic 

 control is absent in insufficient and the artificial introduction of the 

 ; irj parasites seems, to the minds of many, the final solution 



of the problem of control. A.nd doubtless this is so if it is clearly 

 realised that parasites will onl\ control a species, that is to say, they 

 will normallj keep down its numbers, but they will not exterminate it 

 'her. For in practice parasitism does not seem able to 

 deal with more than about 75 per cent, of the total number 

 of any destructive insect. It parasites are present in such large 

 numbers that a very high percentage ol the host must be attacked 

 to enable all the parasites to lay their eggs, they are compelled to 



