THE SILKWORM 69 



them. The natural food of the silkworm was no doubt the 

 leaves of the white mulberry, on which it thrives best. The 

 black mulberry of Persia and other northern countries, which 

 bears the well-known fruit, may also be used as the food-plant, 

 but the quality of the silk is impaired thereby. Long domesti- 

 cation has made the silkworms dependent on the protection of 

 man.. They have lived so long under shelter that the cater- 

 pillars cannot keep their hold when exposed to wind ; they do 

 not know how to screen their bodies from sun or rain, nor how 

 to escape insect and bird enemies. They will often bite 

 through the base of the leaf upon which they are feeding, and 

 so fall to the ground; some are incapable of remounting 

 the tree from which they have fallen, or even of passing 

 from leaf to leaf The wings of the female moth are 

 imperfectly expanded, and she does not attempt to fly. 

 This is common in wild Bombycidse, and is no mark of arti- 

 ficially induced degeneration. But the males are almost as 

 incapable of flight as the females ; at most they are able to 

 flutter downwards, never upwards. In a wild species such 

 inactivity in both sexes would soon lead to total extinction. 

 Attempts have been made to accustom silkworms to live in the 

 open air, and there are some indications that persistent experi- 

 ment and selection might restore the hardiness and vigour 

 which this insect no doubt enjoyed when leading a free life. 

 Where silkworms are reared for curiosity, the quality of the 

 silk being neglected, lettuce-leaves are commonly used for 

 food. They will also eat nettle and oak, but do not thrive on 

 them. Silkworms require either a warm climate or artificial 

 heat. Even in Italy and southern France they require pro- 

 tection from the cold, and the eggs do not hatch spontaneously 

 in spring. Many attempts have been made to introduce silk- 

 growing into new countries. England, Ireland, Denmark, 

 Sweden, Virginia, Pennsylvania, California, Mexico, all in their 

 time entered upon this industry with great hopes, which were 

 doomed to utter disappointment. Cheap labour is as neces- 

 sary as a genial climate and a suitable food-plant. So far the 

 only countries which meet all the conditions of silk-growing 

 are China, Japan, Bengal, France, Italy, and Asia Minor. 



In southern France the silkworms are reared in special 

 buildings (magnaneries) which are well - ventilated and care- 

 fully warmed, the air being frequently tested by thermometers 



