SPINNING CATERPILLARS. 313 



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 com- 

 plete envelope or shroud. Wc have already seen, in 

 the preceding pages, several striking instances of this 

 operation, when, probably for the purpose of husband- 

 ing a scanty supply of silk, extraneous substances are 

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

 pillars, silk is the only material employed. 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 somewhat minute details, though 

 it would require volumes to incorporate all the in- 

 formation 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 ti mperature in which the eggs have been kept 

 during the winter. When the heat of the apartment 

 has been regulated, the first moulting takes place on 

 the fourth or fifth day after hatching, the second 

 begins on the eighth day, the third takes up the 

 thirteenth and fourteenth days, and the last occurs 

 * Cours d' Agriculture, par M. Hozier. Paris, 1801. 



