ii.] CATERPILLARS COLORS OF. 45 



changes its form ; after this it becomes a pupa, without 

 any remarkable peculiarities. Finally, after these won- 

 derful changes and adventures, in the month of August 

 the perfect beetle makes its appearance. 



In fact, whenever in any group we find differences in 

 form or color, we shall always find them associated with 

 differences in habit. Let us take the case of caterpillars. 

 The prevailing color of caterpillars is green, like that 

 of leaves. The value of this to the young insect, the 

 protection it affords, are obvious. We must all have 

 observed how difficult it is to distinguish small green 

 caterpillars from the leaves on which they feed. When, 

 however, they become somewhat larger, their form be- 

 trays them, and it is important that there should be 

 certain marks to divert the eye from the outlines of the 

 body. This is effected, and much protection given, by 

 longitudinal lines (Fig. 35), which accordingly are found 

 on a great many caterpillars. These lines, both in color 

 and thickness, iriuch resemble some of the lines on leaves 

 (especially those, for instance, of grasses), and also the 

 streaks of shadow which occur among foliage. If, how- 

 ever, this be the explanation of them, then they ought 

 to be wanting, as a general rule, in very smal] cater- 

 pillars, and to prevail most among those which feed on 

 or among grasses. Now, similar lines occur on a great 

 number of caterpillars belonging to most different groups 

 of butterflies and moths, as you may see by turning 

 over the illustrations of any monograph of the group. 

 They exist among the hawk-moths, as, for instance, 

 in the humming-bird hawk-moth ; they occur in many 

 butterflies, as, in Arge galatliea, which feeds on the 

 cat's-tail grass ; and in many moths, as, for instance, 



