76 BRITISH LEPIDOPTERA. 



CHAPTER VIII. 



THE PROTECTIVE COLORATION AND DEFENSIVE STRUCTURES OF 

 LEPIDOPTEROUS LARVJE. 



We have already, incidentally, referred to the fact that the exposed 

 life led by many lepidopterous larvae, renders them very liable to be 

 attacked by ichneumons, and to be preyed upon by various mammals, 

 birds, reptiles, and carnivorous insects. We have also shown that they 

 have undergone considerable modification, both for the purposes of con- 

 cealment and defence. For the former, we have seen (ante, p. 43) that 

 larval colours are often modified, probably by phytoscopic influences, and 

 that natural selection has produced specialised patterns, by means of 

 which the larvae are suitably coloured to escape detection in the 

 environment in which they are placed. For the purpose of protection, 

 we have noticed how the simple hairs of the generalised setae (ante, p. 45), 

 and the fine clothing of the skin (ante, p. 38), may be respectively modi- 

 fied into dense hairy fascicles and a thick clothing of hair, which render 

 the larvae quite inedible to many entomophagous animals. We know, 

 also, that the tubercles themselves may be modified into chitinous, 

 prickly spines (as in the Vanessid, Saturniid, and many otherwise 

 widely different, larvae), which serve as a defence for the caterpillars 

 against many of their enemies. 



It may be here remarked that, since the larva leads an independent 

 and entirely different mode of existence from that of the pupa and 

 imago, it often happens that for the successful continuation of a species, 

 a high degree of specialisation is necessary in the larval stage, and 

 that the necessary modification has taken place without a corresponding 

 specialisation of the other stages egg, pupa, or imago. Conversely, 

 it is conceivable that a highly specialised condition may be necessary 

 in either of these stages, whilst the larva remains in a more generalised 

 condition. It is, however, our intention to exclude the consideration 

 of these latter contingencies at present, and to confine ourselves to 

 those specialisations, defensive and offensive, which larvaa have de- 

 veloped for the purpose of protection. 



We may premise, then, by stating that larva? are protected in a 

 variety of ways. They have, in many cases, adopted various habits 

 of concealment when not feeding. Hesperid and Tortricid larvae twist 

 up leaves, Crambid larvae make silken galleries ; many gregarious 

 larvae (such as those of Eriogeuter, Malacosoma, Cnethocampa, etc.) 

 spin silken webs, and these live therein whilst others (as ]>n>/>ana, 

 Pyrameis, etc.) spin leaves together, and dwell in the tent thus formed ; 

 others, again, feed only by night, some drop to the ground, and 

 others throw themselves about violently, when disturbed. We have 

 already noticed (ante, pp. 43-44) by what processes they have become 

 specialised in colour, so as to resemble the leaves among which they 

 rest. One of the most general forms of ornamentation of grass- 

 feeding larvae, is a series of longitudinal lines. These produce an 

 effect resembling the lines of light and shade resulting from the 

 illumination of a grass leaf, and due to the parallel venation of the 

 leaf. Similarly, other larvae are specialised in colour to resemble the 



