266 THE INSECT WORLD, 



It is in this way that the caterpillars let themselves fall from the top 

 of the highest trees : they remount again with no less ease. 



Let us listen to Reaumur's description of the means employed by 

 this caterpillar to ascend these heights. Figs. 260 and 261, drawn, 

 as the three preceding ones, from the plates in Reaumur's Memoir, 

 help us to follow the explanation given by the illustrious naturalist of 

 the evolutions of our little acrobat : — " To remount," says Reaumur, 

 " the caterpillar seizes the thread between its jaws, as high up as it 

 can ; as soon as it has done this it twists its head round, lays it over 

 on one side, and continues to do so more and more every moment 

 Its head seems to descend below the last of the scaly legs which are 

 on the same side as that to which it is inclined. The truth is, how- 

 ever, that it is not its head which descends, the part of the thread 

 which it holds between its jaws is a fixed point for its head and for 

 the rest of its body ; it is that portion of the back corresponding 

 with its scaly legs which the caterpillar twists upwards ; the conse- 

 quence is that the scaly legs and that part of the body to which they 

 belong then ascend. When the last pair of legs is just over the jaws 

 of the caterpillar, one leg, viz., that which is on the side towards 

 which the head is incHned, seizes the thread and brings it over to the 

 corresponding leg on the other side, which is advanced to receive it. 

 If the head is then raised, which is done immediately, it is in order 

 that it may seize the thread at a higher point than that at which it 

 was caught at first ; or, which is the same thing, the head, and con- 

 sequently the whole body of the caterpillar, is found to have ascended 

 to a height equal to the length of the thread which is between the 

 place where its jaws seized it the first time and that where they 

 seized it the second time. The first move in the upward direction is 

 thus made, and the second soon follows. ... If you were to 

 seize the caterpillar on its arrival at the end of its upward journey, 

 you would see a packet of threads huddled together between the 

 four hindmost of the scaly legs. The greater the height ascended 

 the greater is the size of this packet. All the turns of the thread 

 which compose it are entangled. So the caterpillar does not con- 

 sider it of any value. As soon as the insect can walk it gets rid 

 of the mass, sets its legs free, and leaves it behind before one or 

 at most two steps have been taken. The cord is wasted on each 

 ascent, but the caterpillar can afford to lose as many as it likes, 

 for it has in itself the source of the matter necessary for the com- 

 position of the thread, and it is a source from which that which was 

 drawn off is being continually re-supplied. Moreover, spinning the 

 thread costs the caterpillars but little ; indeed, the loopers economise 



