608 TEXT-BOOK OF ENTOMOLOGY 



c. Growth and increase in size of the larva 



The rapidity of growth and enormous increase in size in early 

 life is especially noticeable in caterpillars and other phytophagous 

 larvae. The latest observations are those of Trouvelot on Telea 

 polyphemus. When this silkworm hatches, it weighs ^j- of a grain. 



When 



10 days old it weighs a grain, or 10 times the original weight. 



20 " " 3 grains 60 " " 



30 " " 31 " 620 " " 



40 " " 90 " 1800 



50 " " 207 " 4140 



" When, " he says " a worm is 30 days old, it will have consumed 

 about 90 grains of food ; but when 56 days old, it is fully grown and 

 has consumed not less than 120 oak leaves, weighing f of a pound; 

 besides this it has drank not less than 1 an ounce of water. So the 

 food taken by a single silkworm in 56 days equals in weight 86,000 

 times the primitive weight of the worm. Of this about \ of a 

 pound becomes excrementitious matter, 207 grains are assimilated, 

 and over 5 ounces have evaporated." a 



Dandolo stated that the Asiatic silkworm (Bombyx mori~) weighs on hatching 

 not over T ^ ff of a grain, but when fully grown about 95 grains. During this 

 period, therefore, it has increased 9500 times its original weight, and has eaten 

 60,000 times its weight of food. Newport thought this estimate of the amount 

 of food was a little too great. But comparing it with Trouvelot's estimate for 

 the American silkworm, which weighs when hatched five times as much, it 

 would not appear to be so. Newport found that the larva of Sphinx ligustri at 

 the moment of leaving the egg weighs about ^ of a grain, and when fully fed 

 125 grains, so that in the course of 32 days it increases about 9976 times its 

 original weight. This proportion of increase is exceeded by the larva of Cossus 

 ligniperda, which, boring in the trunks of trees, remains about three years in 

 the larva state, and increases, according to Lyonet, to the amount of 72,000 

 times its first weight. 



Newport adds that those larvae in which the proportion of increase is the 

 greatest, are usually those which remain longest in the pupa state, as in the 

 silkworm. " Thus Redi observed in the maggots of the common flesh-flies a 

 rate of increase amounting to about 200 times the original weight in 24 hours, 

 but the proportion of increase in these larvae does not at all approach that of 

 the Sphinx and Cossus." From his observations on the larva of one of the 

 wild bees (Anthophora retusa) Newport believes that this is also the case with 

 the Hymenoptera. The weight of the egg of this insect is about T i ff of a grain, 

 and the average of a full-grown larva 6 T 8 ff grains, so that its increase is about 

 1020 times its original weight; "which compared with that of the Sphinx of 

 medium size, is but as 1 to 9|, and to a Sphinx of maximum size only as 1 to 

 a little more than 11." 



l Amer. Naturalist, i, p. 85, 1867. 



