264 THE SCHOOL OF REAUMUR 



food, so long as food is required. The tortrix, screened 

 from view by the outer turns of its green case, is able to 

 devour the inner turns at its leisure. 



These small larvae are not strong enough to roll an 

 oak leaf without artifice ; moreover the leaf must not 

 only be rolled, but hindered from unrolling again. In 

 case of attack by a more powerful enemy, the larva 

 must have a ready way of escape not too obvious to the 

 pursuer. All these requirements are met by the instincts 

 of the leaf- rolling tortrix. 



A leaf is generally chosen which has some tendency 

 to curl, and silken threads are spun across the biglit. 

 The threads are not scattered at hazard, but collected 

 into short, stout bands, each of a hundred or more 

 separate filaments. While spinning, the larva swings 

 its head and the fore part of its body to and fro. When 

 the band is half finished the larva climbs upon it, and 

 then proceeds to spin the second half. Its weight, as 

 Reaumur explains, slightly deflects the first mass of 

 threads, and so tightens a little the folded edge of the 

 leaf; the new filaments secure it in its position.^ Each 

 new band does something to increase the tension, and as 

 row after row is added, what was at first a slight con- 

 cavity becomes a close spiral, the turns being just so 

 far separated as to allow the caterpillar to move easily 

 between them. It is thus enabled to spin fresh bands, 

 to feed upon the inside of its tube, and to conceal itself 

 from an enemy. Now and then a main rib is gnawed 

 through in two or three places to make it more flexible. 



When alarmed the larva throws its body into rapid 



1 De Geer {Hist. Nat. des Insectes, Vol. I, p. 425 foil.) thinks that the weight 

 of the larva is too inconsiderable to produce much eflfect. He remarks that the 

 larva pulls the last-spun threads towards its body with its hooked feet. Every 

 new thread visibly draws the edge of the leaf inwards, and all the old threads 

 are lax. 





