68 INJURIOUS AND USEFUL INSECTS 



be painted to a height of four or five feet, and petroleum- 

 emulsion poured upon the earth about the base of the 

 trunk. Badly infested trees should be felled and split, all 

 caterpillars lurking in the wood being destroyed at the same 

 time with wires. The green woodpecker is useful in keeping 

 down the numbers of the goat-moth, and its stomach is 

 sometimes filled with the larvae. 



17. THE SILKWORM (Bombyx mori) 



Though the silkworm is not native to Britain nor to any 

 part of Europe, and though all attempts to acclimatise it 

 in England have failed, it is an insect so important to industry 

 that we feel bound to give some account of it. The insects 

 which are directly serviceable to man are few, and not a single 

 one is indigenous to our northern countries. First in im- 

 portance come the hive-bee, and the silkworm. Next, 

 but distinctly inferior to the first class in usefulness, we 

 should place the cochineal-insect, and the lac-insect. After 

 these there seems at first sight nothing worth mention, except 

 perhaps the blister-beetles, the few insects which are used as 

 food, mostly by savage races, and the insects used as bait by 

 the angler. But we are overlooking infinitely greater benefits 

 received from insects than any which we derive from their 

 bodies or their secretions. A large proportion of our flowers 

 depend upon the visits of insects for the setting of their seeds, 

 and among these flowers are many of great practical importance, 

 fruit-trees, forage-plants, and vegetables. Insects constitute the 

 sole food of large tribes of birds, and some part of the food of 

 nearly all. Were it possible to exterminate all insects except 

 such as are known to be directly profitable to man, we should 

 lose many an agreeable fruit, many a beautiful flower, and 

 most of our song-birds. The daily life of the artisan and the 

 labourer would be impoverished, as well as the studies of the 

 biologist. 



The silkworm is now known only as a domestic species. 

 It is native to China, and probably as a wild species inhabited 

 the mountainous regions of Northern China. Though intro- 

 duced long ago to Japan, India, and other countries bordering 

 on China, we have no proof that it was indigenous in any of 



