10 



INSECTS : THEIR STIiUCTUEE AND FOOD. 



Food. 



From the moment that an insect hatches^ its first task is to provide 

 food by its own exertions ; it has also to escape the enemies and dangers 

 that surround it ; lastly, it has to lay eggs in the proper situation and in 

 some cases must provide for the young. These are the three prime neces- 

 sities of the insect^s life, and though in many cases it is possible that the 

 gratification of a taste for other pleasures is an object in life, we may 

 interpret the activities, the form, colour and structure, even the life 



history of insects in terms of these three 

 principal needs. 



The food of insects is extremely diverse, 

 and it is not always clear how they are able 

 to extract the requisite amount of nutriment 

 from the substances they consume. We may 

 at once abandon the idea that nutrition is 

 comparable to that of domestic animals. 

 Digestion, nutrition and respiration are very 

 different in insects. What proportion of 

 proteids, carbohydrates and fats is necessary 

 cannot be stated. The amount of food or of 

 air necessary to existence may be reduced 

 to very low limits since insects are not 

 Fig. 16. warm-blooded ; in the absence of muscular 



Wingless Perfect Insect : the activity there is probably uo wastage of the 

 insect lives on the surface of the . •• it „^,r^-„-, n/^ 



sea and has no need of toings. tissues, no consumption of oxygcn, no 

 {From Distant) elimination of water or of waste |)roducts. 



The amount of food or oxygen assimilated may be measured by muscular 

 activity and may cease entirely when this ceases. Bearing this in 

 mind, we need not be astonished at the insects which live solely in 

 dry wood, in burrows without access to the air, or which feed solely on 

 chillies, opium or tobacco. Such insects do not drinlc, they simply eat, 

 and we are entirely ignorant of their digestive and nutritive processes. 

 Nor is it astonishing that many insects can live for many months 

 without food. 



Most insects live on land, a few on or near the sea, many in fr>sh 

 water. Marine insects are few -, some in the sea itself, some on the 

 surface, a larger number on the beach or in rock-pools. Eelatively, the 

 number is very small, and sea water presents an almost impervious 

 obstacle to insect life. Fresh-water ponds, streams, tanks, and other supi^lies 



