CHAPTER ill. 



FORM AND COLOUR. 



JF we examine an insect, we can possibly deduce from its form, 

 structure and colour many facts as to its probable habits and habitat. 

 The complete structure of an insect, as well as its life history, is inti- 

 mately correlated with the predominating motives of its life, search for 

 food, escape from enemies, reproduction of the species. 



In all insects the modifications of form and colour which are cor- 

 related with sex and reproduction appear only in the imago stage. 

 Larvae are of no sex and even the larger nymphs of the OrtJioptera 

 display only minor sexual differences, the sexual characters not being 

 matured until the final moult. In the higher insects the search for 

 food is confined to the larval stage, not wholly but very largely. We may 

 regard the division of the life of an insect into distinct periods, in one of 

 which the search for food is the principal business, in the other repro- 

 duction, as a valuable adaptation, which may account for the success of 

 the insect group over others. 



In nearly all insects the necessity of special devices for offence or 

 defence lasts throughout the entire life. The exceptions are the insects 

 which live hidden, such as the borers ; with these exceptions, every 

 insect must be protected from foes, and in all stages we find that there 

 are numberless special contrivances for securing immunity. 



It is impossible to discuss fully the varieties of form and colour 

 found in insects. There is a meaning in the colour scheme, the details 

 of the structure, the general form and appearance of every species, which 

 we could find if we were fully acquainted with its habits. We are only 

 slightly acquainted with the lives of any insects, and most live in ways 

 totally unknown to us. It is possible only to outline a few generalities, 

 principles that, extend over large groups of insects and give us a clue 

 to the method of understanding the significance of form and colour in 



insects* 



Size. 



The general conception of the size of an insect is perhaps of some- 

 thing about as large as a bean or larger. The majority of species are, 

 however, less than one quarter of an inch long; it is misleading to 

 judge from our observation of insects^ since the larger ones catch the 

 eye, are more easily studied and far more easily preserved, whilst the 

 smaller insects escape notice and are passed by. 



