THE EVOLUTION OF THE CATERPILLAR 623 



very young the caterpillars content themselves with the com- 

 paratively soft tissue beneath the bark, but gradually extend 

 their operations — there being generally a pretty extensive 

 colony in each tree — until the whole of the ligneous portion is 

 honeycombed with their burrows. In advanced stages, borings 

 often come closer to the surface and sap exudes freely, this 

 being mixed with an excretion from the caterpillars, which 

 gives it a most peculiar odour, said to resemble that of he- 

 goats (whence the name) but to my mind quite distinctive 

 and only slightly similar. In any case, it is very powerful, 

 and I have generally located goat-ridden trees by perceiving 

 this odour — often a considerable distance away. 



The goat caterpillar shows a striking departure from other 

 borers in its colour, which is dull flesh, the back being dark 

 red, almost mahogany-hke in colour. It seems reasonable to 

 suppose that this is associated with its choice of tree, for it is 

 not very different from that of the wood of many oaks, and the 

 larvas are not easily seen among the debris if they remain still. 

 It need scarcely be pointed out that these and other wood- 

 boring insects are liable to fall a prey to birds — woodpeckers, 

 for example — and it is manifest that even a slight resemblance 

 to the wood must afford a measure of protection. 



Many well-accredited stories of the power of the Goat Cater- 

 pillar's jaws have been told. In one case, a collector placed 

 a number in a cigar-box, which he stood on the piano. During 

 the night, one gnawed through box and piano and was found 

 wandering in the interior the next morning. An even more 

 remarkable case has the unimpeachable authority of the late 

 Prof. Henslow. He says : "I placed half a dozen cater- 

 pillars of the goat-moth in a glass jar, with sawdust and a 

 piece of willow, and covered the mouth with sheet lead, which 

 was perforated with an awl to admit the air. Three of the 

 caterpillars were found crawling on the floor, and on examin- 

 ing the jar I found they had effected their escape by gnawing 

 the lead, having enlarged two of the perforations sufficiently 

 to enable them to pass out of their prison." 



IV 



The Goat Moth, widely though it differs in size, is linked 

 with another interesting group of caterpillars, which have 

 contrived to evade the risks of feeding in the open in an ex- 

 ceedingly ingenious way, by the familiar Codlin Moth, a small 

 species whose larva is only too frequently found in the interior 

 of apples and is, therefore, a true borer. The great mass of 

 the Tortrices, to which tribe this belongs, are distinguished 

 by their habit of rolling the leaves of the plants on which they 



