SPINNING CATERPILLARS. 273 



large and heavy, spins a thick web on the upper surface of 

 a leaf, to which it adheres till the change is effected. 



The most important operation, however, of silk-spin- 

 ning is performed before the caterpillar is transformed into 

 a chrysalis, and is most remarkable in the caterpillars of 

 moths and other four-winged flies, with the exception 

 of those of butterflies ; for though these exhibit, perhaps, 

 greater ingenuity, they seldom spin more than a few 

 threads to secure the chrysalis from falling, whereas the 

 others spin for it a complete envelope or shroud. We 

 have already seen, in the preceding pages, several striking 

 instances of this operation, when, probably for the purpose 

 of husbanding a scanty supply of silk, extraneous substances 

 are worked into the texture. In the case of other cater- 

 pillars, silk is the only material emploj^ed. Of this the 

 cocoon of the silk-worm is the most prominent example, 

 in consequence of its importance in our manufactures and 

 commerce, and on that account will demand from us some- 

 what minute details, though it would require volumes to 

 incorporate all the information which has been published 

 on the subject. 



Silk-Worm. 



The silk-worm, like most other caterpillars, changes its 

 skin four times during its growth. The intervals at which 

 the four moultings follow each other depend much on 

 climate or temperature, as well as on the quality and 

 quantity of food. It is thence found, that if they are 

 exposed to a high temperature, say from 81^ to 100° 

 Fahrenheit, the moultings will be hastened ; and only five 

 days will be consumed in moulting the third or fourth 

 time, whilst those worms that have not been hastened take 

 seven or eight days.* 



The period of the moultings is also influenced by the 

 temperature in which the eggs have been kept during the 

 winter. When the heat of the apartment has been regu- 

 lated, the first moulting takes place on the fourth or fifth 



Coiirs d'Agriciilture, par M. Eozier. Paris, 1801. 



T 



