1908] Habits of Insects as a Factor in Classification 79 



Of the Lepidoptera comparatively few gall makers are known, 

 but amongst the tineids we find gradations from miners to gall 

 makers. 



Among the sawflies there are several genera which live entirely 

 in galls and here again quite complete gradations may be observed 

 from the more general mode of life to the distinctly gall making 

 form. The most distinctly gall making group, the Cynipids, 

 presents us also with almost every possible gradation from the 

 simple attack on leaves to the formation of very elaborate gall 

 structures, and by careful comparison of different forms we can 

 trace with considerable sureness the lines of divergence for each 

 of the species and their relative departure from primitive forms. 



WOOD BORING INSECTS AND BARK BEETLES. 



Of the insects that work into the substance of w^oody plants 

 we have a considerable number, and many of them illustrate a 

 long course of adaptation to this particular form of life. The 

 termites show an extreme ability to tunnel into wood and devour 

 the interior of large masses of woody structures, and for this pur- 

 pose have the mouth parts considerably specialized. The habit, 

 however, is associated with the community habit which is dis- 

 cussed under another head. Among the Lepidoptera we have 

 several families in which this mode of life has been quite fully 

 developed, the most striking forms being the Cossidae including 

 the large carpenter moths, the larvae of which tunnel deeply into 

 various hard wood trees, and the Sesiidce, practically the entire 

 family being specialized for this habit. It shows, however, con- 

 siderable degrees of adaptation, the peach borer living mainly 

 just beneath the bark in shallow cavities w^hich may open to the 

 surface, while in the Syringa borer. Currant borer and some others, 

 the central portion of the stem or trunk of the tree is invaded. 

 Among the beetles the family of long horned borers (Ceramby- 

 cidee) is among the most characteristic, and excepting a few 

 forms such as the milk weed borers are adapted for penetrating 

 deeply into very hard wood. The Hickory borer for example 

 tunnels into the heart wood of Hickory, requiring a period of two 

 or three years for its growth. The Locust borer. Poplar borer, 

 and the familiar Apple borer are other well known examples. 

 Again in the Buprestidas we have a distinctly wood boring group, 

 although in these the borers are usually confined to the younger 

 wood or cavities beneath the bark. They show perhaps less 



