INSECTS. 



201 



examination shows that these parts are covered with fine striations, and 

 hence the noise in its character resembles that produced by rubbing a fine 

 file with a quill. 



With us most of the weevils are small, inconspicuous forms, but in the 

 tropics are species which rival the long-horns in size and beaut}'. Possibly 



Fig. 190. — Long-horned weevil (Xenoceros). 



the best known of these tropical forms is the celebrated diamond-beetle of 

 Brazil; a brilliantly green-colored form from an inch to an inch and a 

 quarter in length. In reality the beetle is black, and the colors are due to 

 the scales which line the shallow pits on the surface. These scales are 

 finely striated, and the color is produced by diffraction exactly as in the 

 case of the pearl-oyster. There are several thousand species of weevils 

 known, all of which are injurious to vegetation, but of all this number we 

 can mention but two or three. 



Best known of all the series are the pea and bean weevils, of which 



Fig. 191. — Bean and pea weevils (Bruchus), enlarged; the lines at the sides of each show the natural size 



of the beetles. 



three species are shown in our cut. It should be noticed that the figures 

 of the insects are enlarged, while those of the plants arc of the natural 

 size. The true length of each beetle is shown by the hair-line at the side. 



