Insects and their world 



other hand, may have larvae that are quite different in structure and 

 habits from their parents : e.g. a caterpillar and a butterfly. 



Whether metamorphosis is gradual or sudden, the young stages need 

 food for growth and metamorphosis, while the adults need food for 

 reproduction and associated aaivities such as mating swarms and egg- 

 laying. Here, again, it is the insects like aphids and grasshoppers that 

 have the easier time, because they spend their lives among their own 

 kind, amidst an abundance of food (Fig. 20). It is the insects that 

 emerge from a pupa and then fly away that have the difficult problem 

 of finding food in new surroundings, mating, and then returning to the 

 breeding-ground to lay their eggs. At first sight we might wonder how 

 the holometabolous insects came to evolve into a way of hfe that seems 

 to be both difficult and precarious, but apparently the evolutionary 

 advantages of greater mobility, and more rapid spread by finding new 

 breeding-grounds, must offset the hazards of adult life in these groups. 



Occasionally, as in the mayflies (Order Ephemeroptera) and the 

 non-biting midges (Order Diptera: family Chironomidae), the young 

 form, whether nymph or larva, stores enough food to serve the adult as 

 well, and the latter does not need to feed. It has poor mouthparts, or none 

 at all, and its short life is devoted entirely to mating and egglaying. 



Insects make use of all kinds of food, plant or animal, fresh or de- 

 cayed, but their methods of feeding may be grouped into two main 

 kinds. Either they bite and chew, or they suck, piercing if necessary to 

 obtain hquid food. Most often all the insects of one Order are com- 

 mitted to one or other of these two types, even though there may be 

 many variations in detail. 



Thus Orthoptera (Fig. 25a) and their near relatives bite and chew 

 at all stages, whether they are plant-feeders Hke the locusts, feed on 

 scraps like the cockroaches, or catch other insects, like the mantids. 

 Heteroptera (Fig. 25d) and Homoptera, on the other hand, all 

 pierce and suck : mostly they suck the juices of plants, but some have 

 adapted the same mechanism to sucking the blood of other inseas — 

 like the Reduviidae, and the various water-bugs — or the blood of verte- 

 brates — Hke the bed-bugs (Cimicidae) and the bat-bugs (Polyctenidae). 

 Once again we see that the Hemimetabola, with their continuous 

 development, generally keep the same feeding-habits in young and adults 

 alike. The larvae of the Holometabola, hving a Hfe quite cut off" from 

 that of the adult, may have totally different mouthparts. Thus larvae of 

 Lepidoptera (caterpillars) bite and chew the leaves of plants, as any 

 gardener knows; adult butterflies and moths have lost the ability to 

 chew, and instead suck Hquid food through a coiled tube formed from 

 the maxiUae. 



42 



