20 
INSECTS IN GENERAL. 
DIFFERENCE OF FOOD OF THE LARVA AND THE PERFECT INSECT. 
Iu attempting to classify insects according to the nature of their food 
■we meet with a peculiar difficulty, owing to the remarkable change 
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 upon the 
honey of flowers, or other liquid substances. Some two-winged Hies 
(Asilidce) 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 (Meloidw), which are 
parasitic in their larva state, but subsist upon foliage after they have 
assumed the beetle form. The question therefore arises, to which stage 
of the insect’s existence shall the precedence be given in this respect ? 
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 in 
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 pre- 
cedence. v • 
In the following work. I have not thought it best to adopt any inflexi- 
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 ol ani- 
mal lice. The insects which attack man directly are annoying rather 
than seriously hurtf ul, 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. 
