Injurious to Vegetation," p. 222) says of one species, which inhabits the 

 locust tree: "They never sit across the limbs, but always in the direction 

 of their length, with the head or fore part of the body toward the extremity 

 of the branches. On account of their peculiar form, which is that of a thick 

 cone with a very oblique direction, their dark color [without obliterative shad- 

 ing], and their fixed posture while perching, they would readily be mistaken 

 for the thorns of the tree ..." Such mimicry of excrescences on twigs is 

 probably common to many members of the Tree Hopper family. Some, 

 however, have patterns which cannot well lend themselves to a simple mimetic 

 resemblance, and whose effect must tend rather toward obliteration. The 

 little Leaf Hoppers (TettigoniidcB, etc.) are often very bright-colored — green 

 and red and yellow, in sharp, clear patterns — like tiny parrots. The effect 

 of this motley coloration, against flower-, leaf-, and stem-surfaces, is of course 

 obliterative — especially as the little hoppers are also counter shaded. Very 

 likely, however, there are also definite mimetic developments among them. 

 Plant lice or aphides {Aphidida) are of various tints, from dark brown and 

 grayish black to fair, translucent green. As a rule, their color closely matches 

 that of the plant surface on which they habitually feed and rest. Some of them 

 are blotched or speckled, but few or none, I believe, have truly elaborate 

 patterns. Nor do their costumes show more than a slight tendency toward 

 obliterative shading, although the actual translucence of some kinds nearly com- 

 pensates their lack of this device ( — ^both weakening or even obliterating the 

 light-and-shade of their own bodies, and preventing their casting shadows 

 on the leaf- or flower-surfaces on which they sit). Some, in their early life, 

 are cloaked — and, likely enough, protected, though certainly they are not 

 conceded — ^by a covering, sometimes enormously developed, of white, soft, 

 cottony down. These white-tufted bark lice are a familiar sight on willow 

 and alder bushes. 



Many other forms of hemipterous (and especially homopterous) insect 

 might be mentioned, but mainly to show their general dinginess of coloring, 

 which seems in keeping with their habits. Many of them are nocturnal and se- 



203 



