178 



THE EVOLUTION THEORY 



Fig. 115. Caterpillar of the Humming biid 

 Hawk-moth, Macroglossa stellcdarum. sbd, the sub- 

 dorsal line. 



caterpillars of hawk-moths or Sphingidae — longitudinal striping, 

 obliquely transverse striping, and spots. Longitudinal striping pure 

 and unmixed is now found only in a few species, for instance 

 in the caterpillar of the Macroglossa stelhdariim (Fig. 115), in 

 which a white longitudinal line, beginning at the tip of the tail, 

 runs up each side of the body to the head as a ' subdorsal stripe ' 

 (sbd). These, with other two similar stripes, effectively secure 



the fairly large caterpillar 

 from discovery when it is 

 among grass and herbs. 



Transverse striping occurs 

 as the sole mode of marking 

 in species which live on bushes 

 and trees whose leaves have 

 strong lateral veins, such as 

 willows, poplars, oaks, privet, syringa, and so on, and these markings 

 associated with the leaf-green of their colouring protect them most 

 effectively from discovery. 



The third scheme of marking, namely by spots, occurs in various 

 forms in species of the genera DeilepMla and Cheer ocampa, and it 

 varies in its biological significance ; in many species the spots serve 

 as a warning colour, by making the caterpillar conspicuous and easily 

 seen from a distance {DeilepMla galii, Fig. T17); in others they 

 imitate the eyes of a larger animal, and have a ' terrifying ' effect, 

 as we have already said (Fig. 4) ; in still other and rarer cases they 



heio'hten the resemblance 

 of the caterpillar to its 

 food -plant by mimicking 

 parts of it, as, for instance, 

 the red berries of the 

 buckthorn (Deilephila 

 liippopliaes, Fig. 8, r). 

 Thus all three modes 

 of marking possess a biological value, and protect the soft and 

 easily wounded animal in some way, and, in the case of at least 

 two of them, it is clear that they must have arisen at the very 

 end of the caterpillar's development, since they can only be effec- 

 tive as the animal is approaching full size, and would be valueless 

 in the very young caterpillar. The transverse striping only makes 

 the caterpillar like a leaf when the stripes bear about the same 

 relation to each other as those on the leaf, and eye-spots can only 

 scare away lizards and birds when they are of a certain size. Only 



Fig. 3 (repeated). Full-grown caterpillar of the 

 Eyed Hawk-moth, Smerinthus oceUatus. sb, the sub- 

 dorsal stripe. 



