244 M. Huber on the Habits of a Saw-fly. 



that the rolling caterpillars make cylinders with leaves, whereas 

 in the present case the rolling up must be oblique in order to 

 produce a spiral, and this, probably, is what renders necessary 

 the complex process which the larva of the Saw-fly of the 

 hazel employs. 



The axis of the cone or case of our larva is frequently placed 

 at right angles to the tangent which might be drawn at the 

 edge of the leaf; yet the orifice is not parallel to this edge ; 

 on the contrary, this opening is very oblique, and such as it 

 should be in order that the band of which it is formed in roll- 

 ing up may only cover over the last spiral by its edge, so as 

 to form a prolongation of the case, and not a simple coating. 



It sometimes happens that this larva, whether by chance 

 or by design, detaches its case from the leaf: this especially 

 occurs when the leaf withers ; for then it is obliged to seek for 

 a fresher one, a thing which frequently happened to those 

 which I had under my observation at home. I have often 

 amused myself by cutting the little bands and suspending the 

 case underneath the leaf, by means of some one of the scattered 

 silks which remained at the mouth, as the larva itself does 

 w T hen its case is wholly finished. But I operated before the 

 time, and it had still several whorls to add to its cone : had I 

 left but a single thread, it would have been sufficient to bring 

 back its case towards the leaf, for this larva, of a slender form, 

 is gifted with an unequalled agility and suppleness. Coming 

 more than three-fourths out of its cone, it bent itself in a 

 thousand ways, and by its skill succeeded in reaching the leaf, 

 to which it fastened some imperceptible threads of silk ; it 

 clung to these threads, then drawing its body forwards, it 

 made the case approach the leaf by help of the side legs and 

 the two processes near its hinder extremity ; then bound it 

 with new and shorter threads of silk, so that it nearly touched 

 the lower surface of the leaf. 



The cone had now to be made to travel in this situation. 

 The process which it employs is most ingenious : it leans for- 

 ward out of its case on the side to which it intends to direct 

 it, and, as far as it can reach, stretches threads of silk from 

 the leaf to the case. This latter, held back by former threads, 

 does not as yet move at all ; but the caterpillar, with its accus- 

 tomed ingenuity, cuts the former threads with its jaws ; if they 

 resist too much, it stretches its body so as to force away the 

 cone, when the last attachments break : in this way the cone 

 is suspended only by the new threads, its centre of gravity is 

 now displaced and is carried forward. A fresh similar man- 

 oeuvre effects a new step ; thus travels this heavy load, sus- 

 tained by threads of silk which are substituted for each other 



