THE COLEOPTERA 99 



The distinctive characters of the group are: 



Insects which as adults nearly always have four wings, the front pair 

 entirely thickened and horny; the hind pair membranous: mouth parts for 

 chewing: body usually rather stout. Metamorphosis complete. 



There is a great diversity in the structure of the antennae in different 

 beetles, and also in the form of the legs and number of tarsal segments. 

 The arrangement of the skeletal plates around the articulation of the 

 fore coxae to the body is also variable and of importance in classification. 



Eggs of the Coleoptera are laid in many kinds of places on leaves, 

 in branches, in decaying matter, water, etc. The larvae which hatch 

 are usually called " grubs" except when they bore in wood. Then, as 

 with larvae of any order found under such conditions, they are termed 

 " borers." They usually have the three pairs of legs which become those 

 of the adult, though these are sometimes wanting. Some feed upon other 

 animals, some on leaves or wood, some on carrion, and others on various 

 substances. After full larval growth has been attained they pupate. 

 The pupal shell or skeleton generally covers the surface of the body 

 closely, but the wings and legs though lying close to it are covered sepa- 

 rately as projecting appendages and not ensheathed by the shell enclosing 

 the body proper. Such a pupa case is called a pupa libera, or free pupa. 

 In some Coleoptera this condition does not obtain, the pupa shell en- 

 closing wings, limbs and body with no projecting appendage sheaths, 

 and such a case is called a pupa obtecta (see Fig. 33). 



The beetles are generally divided as a matter of convenience into the 

 true Coleoptera (Coleoptera genuina or Coleoptera vera) and the Snout 

 Beetles (Rhynchophora), though it is at least doubtful if the latter is a 

 natural group. The insects in this section are easily recognized, in most 

 cases, by having the front of the head prolonged into a snout which may. 

 be long and slender in some cases even longer than the body or short 

 and stout, being sometimes so short as to be hardly noticeable. The 

 antennae arise from the sides of the snout and in most cases have a .bend 

 like an elbow near the middle. The mouth parts are at the end of the 

 snout, but the labrum and both pairs of palpi are absent. The insects 

 of this group are even more firm bodied than the other Coleoptera. 



The true beetles (Coleoptera vera) have no snout. The mouth parts 

 are all present and as a group its members average larger than the 

 Rhynchophora: indeed the largest bodied insects known belong here. 



THE TRUE COLEOPTERA (Coleoptera vera) 



This is by far the larger section of the beetles, more than 75 of the 

 80 odd families belonging here. They vary greatly in structure, habits 

 and food. Many of the families are of little or no economic importance 

 and have few members, while others include a very large number of 

 species, many of wnich are very destructive. 



