62 INSECT ARTIZANS AND THEIR WORK 



this mining habit, and it is easy to find examples 

 on all kinds of plants. It is not even necessary to 

 search for them, for the mines in most cases adver- 

 tise the presence of the miner. This, however, is 

 not the case with one of the most plentiful of all, 

 and one of the most remarkable. We may own 

 a poplar-tree nearly all of whose leaves are tenanted 

 by the caterpillars of Phyllocnistis suffusella, and 

 never suspect the fact. We may see the evidence 

 of their presence, but imagine that a snail or slug 

 had been crawling over all the leaves, leaving a 

 slightly shining track. These tracks are really 

 those of the caterpillar under the upper skin. This 

 larva differs from most of the miners in the fact 

 that he takes no solid food. Strictly speaking, it is 

 perhaps not right to include him among the miners, 

 for all he does is to sever the connection of the 

 upper cuticle and the parenchyma, and instead of 

 eating his way through the latter, he is content to 

 suck up the sap that flows from the severed cells. 

 Upon this liquid fare he subsists entirely. 



When it changes its skin the second time its 

 form is entirely altered, for it develops a bi-lobed 

 tail which gives it a fish-like appearance. At the 

 end of this stadium, as it is termed, the caterpillar 

 has reached the edge of the leaf, where it stretches 

 itself out and appears to die ; but it is only another 

 change. About a day later it has cast its skin 

 again, and now appears in more normal caterpillar 

 form, and white, whereas before it was colourless. 

 It feeds no more, but has assumed its new dress 



