20 INSECTS m GENERAL. 



DIPFERENCE OP FOOD OF THE LARVA AND THE PERFECT INSECT. 



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

 we meet with a peculiar ditliculty, owing to the remarkable cliangc 

 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 butterflies and moths which they produce subsist ui)on the 

 honey of flowers, or other liquid substances. Some two-wiiigcd ilies 

 {Asilidce) feed upon the roots of jilants in their larva state, but become 

 eminently predaceous in their Avinged state. Another renuirkable ex- 

 arai)le is furnished by certain coleopterous insects {Melolda'), which are 

 parasitic in their larva state, but subsist upon foliage after they have 

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

 of the insect's existence shall the precedence be given in this res[)ect '? 

 At first view it would seem that the i>erfect state ought to govern, but 

 when we take into account that insects are comparatively short b'vod iii 

 this state 5 that having arrived at maturity they require but litth', 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 lar\'a 

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

 when we cousidt^r this, it seems more reasonable that in classifving in- 

 sects upon this basis, the food-habits of the larva should take the pre- 

 cedence. 



In the following work I have not thought it best to adopt 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 terras noxious and injurious are often used indiscriminately, but 

 strictly speaking, noxious insects are those which are endowed with 

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

 to two classes accoi-dingly as they are hurtful to mankind din^ctly, such 

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

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

 mal lice. The insects which attack man directly are anno^ ing rather 

 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 properly 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. 



