LEPiriOPTERA. 241 



of food is devoured by these little creatures. One experiment 

 which I made can give some idea of it : when the young silk 

 worm hatches out, it weighs one-twentieth of a grain ; when 



10 days old it weighs 1-2 a grain, or 10 times its original weight. 



20 " " " " 3 grains " 60 " " " " 



30 " " " <• 31 " " 020 " " " " 



40 " " " " 90 " " 1800 " " " " 



56 " " " " 207 " " 4140 " " " " 



When a worm is thirty days old it will have consumed about 

 ninety grains of food ; but when fifty-six days old it is fully 

 grown and has consumed not less than one hundred and twenty 

 oak leaves weighing three-fourths of a pound ; besides this it 

 has drank not less than one-half an ounce of water. So the 

 food taken by a single silk-worm in fifty-six days equals in 

 weight eighty-six thousand times the primitive weight of the 

 worm. Of this, about one-fourth of a pound becomes excre- 

 mentitious matter ; two hundred and seven grains are assimi- 

 lated and over five ounces have evaporated. What a destruction 

 of leaves this single species of insect could make if only a one 

 hundredth part of the eggs laid came to maturity ! A few 

 years would be suflScient for the propagation of a number large 

 enough to devour all the leaves of our forests." The Lepidop- 

 tera are almost without exception injurious to vegetation and 

 are among the chief enemies of the agriculturist. 



They are rarely found fossil owing to the delicacy of their 

 bodies. Remains, doubtfully referred to the Lepidoptera, have 

 been found in the Jura formation. A Sphinx-like moth has 

 been discovered in the Tertiary formation of Europe, and a few 

 minute forms have occurred in Amber. 



Butterflies are easily distinguished from the other groups by 

 their knobbed anteniife. In the Sphinges and their allies the 

 feelers are thickened in the middle : in the Moths they are fili- 

 form and often pectinated like feathers. Lepidoptera have 

 also been divided into three large groups, called Diurnal, Cre- 

 puscular and Nocturnal, since butterflies fly in the sunshine 

 alone, most Sphinges in the twilight (some of them, however, 

 fly in the hottest sunshine), while the moths are generally 

 night-fliers, though many of them fly in the day time, thus 

 showing that the distinctions are somewhat artificial. 



The larger Lepidoptera (butterflies and the larger moths) 

 16 



