20 INSECTS IN GENERAL. 



DIFFERENCE OF FOOD OF THE LARVA AND THE PERFECT INSECT. 



lu attempting to classify insects according to the nature of tlicir food 

 we meet with a peculiar difliculty, owing to the remarkable cliange 

 which some species undergo in this respect, in passing from the larva to 

 the perfect state. Most caterpillars, for example, feed upon leaves, 

 whilst the butteriiies and moths which they produce subsist upon the 

 honey of flowers, or other liquid substances. Some two- winged Hies 

 {Axilidw) feed upon the roots of plants in their larva state, but become 

 eminently predaceous in their winged state. Another remarkable ex- 

 ample is furnished by certain coleopterous insects (Aleloidw), which are 

 I^arasitic in their larva state, but subsist ui)on foliage after they liave 

 assumed the beetle form. The question therefore arises, to which stage 

 of the insect's existence shall the i)recedence be given in this resi>ect'? 

 At first view it would seem that the perfect state ought to govern, but 

 when we take into account that insects are comparatively short lived ui 

 this state; that having arrived at maturity they require but little food ; 

 and that some insects take no food at all at this stage of their lives ; 

 whereas all the growth of an insect takes place whilst it is in the larva 

 state, and consequently it is in this state that they feed so voraciously : 

 when we consider this, it seems more reasonable that in classifying in- 

 sects upon this basis, the food-habits of the larva should take the [)re- 

 cedence. 



In the following work I have not thought it best to ado])t any inllexi- 

 ble rule in this matter, but have been governed by one or the other 

 view accordingly as its importance might seem to preponderate in 

 each particular case. 



DISTINCTION BETWEEN NOXIOUS AND INJURIOUS INSECTS. 



The terms noxious and injurious are often used indiscriminately, but 

 strictly speaking, noxious insects are those which are endowed with 

 some poisonous or otherwise hurtful quality ; and these are divisible in- 

 to two classes accordingly as they are hurtful to mankind directly, such 

 as the mosquito, flea, and bed-bug ; or are hurtful to the domestica- 

 ted animals, as the horse-fly, the bot-fly, and the various kinds of ani- 

 mal lice. The insects which attack man directly are anno.ving rn.ther 

 than seriously hurtful, and this is usually the case also with those which 

 molest the domesticated animals; but these sometimes multiply so as 

 to seriously impoverish the animals which they infest. 



The term injurious^ as distinguished from noxious, is proi)crly applied 

 to all those insects which damage mankind indirectly, but often to a 

 most serious extent, by depredating upon those crops upon which we de- 

 pend for subsistence and profit. 



