194 SOME SOUTH INDIAN INSECTS, ETC. CHAP. XXI. 



Chapter XXI. 

 BENEFICIAL INSECTS. 



'■ The hrsi - inquishing an enemy is to ascertain correctly Is habits; 



ihe next to he so certain ike one party h>r another : and 



a third and no less important objci i is to bi well acquainted with our allies and ft 



Curtis Farm Insects. 

 AFTER bitter experience of the ravages oi insect-pests amongst 

 his crops the cultivator is apt to come to the conclusion that his 

 only safety lies in the prompt destruction of every form of insect- 

 life wherever met with. But indiscriminate slaughter of this sort 

 will do almost as much harm as good for it will result in the des- 

 truction not only of pests but of the innumerable insects of all kinds 

 which help to keep the pots in some control. For. as already 

 pointed out (chapters VUJ X). the possible rate of increase of any 

 insect, in the absence of enemies, is so enormous that in the short 

 space of a few months its numbers would be so vast as to devour 

 every scrap of its foodplant in any given district. 



The inset t enemies oi crop pots, which keep these latter 

 within bounds, may be called the farmer's friends, and indeed 

 they are more than this thc\ are indispensable allies. Insects 

 of this class are gcncralh divided into predators and parasites, 

 predators being animals which are predaceous on others, i.e., which 

 devour other animals which thej capture, whilst parasites have 

 already been defined as organisms which live at the expense and 

 to the detriment oi Othei organisms. The distinction between 

 these two groups is not always verj sharply defined but in practice 

 it is convenient to keep the two classes distinct. Perhaps the 

 difference may be brought out more clearly by the introduction of 

 a time factor, in which case we may say that predators devour 

 their prey forthwith whilst parasites devour it slowl) and gradually 

 and may not always kill it. A beetle or bug which catches a 

 caterpillai and feeds on it forthwith is a predator; a fly which 

 lays its eggs m tin- caterpillar, in and on which the fly's grubs 

 feed at leisure, is a parasite. Parasites may be considered under 

 various headings (hyperparasites, superparasites, etc. I. as already- 

 indicated in chapter YIII. 



Predaceous insects occuj in almost all groups, many insects 

 feeding entirely on others and some which feed normally on dead 

 animal or vegetable matter occasionally devouring living prey; 



