352 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1^19. 
We might continue to cite insect after insect and the birds that feed 
upon them, but one further case will suffice. 
Trouvelot, who introduced the gipsy moth into the United States 
of America, specially studied the American silkworm, and respecting 
its food and rate of growth he made numerous experiments. The 
rate of growth and the amount of food consumed are astonishing. 
Upon hatching from the egg, the caterpillar weighs one-twentieth of 
a grain ; when 10 days old its weight has increased to half a grain, or 
ten times the original weight ; when 20 days old it weighs 3 grains, or 
sixty times its original weight ; when 30 days old its weight has in- 
creased to 31 grains, or six hundred and twenty times the original 
weight; when 40 days old it weighs 90 grains, or eighteen hundred 
times its original weight ; and when 56 days old its weight has risen 
to 207 grains, or four thousand one hundred and forty times the 
original weight. 
When 30 days old this caterpillar will have consumed about 90 
grains of food, but by the time it is fully grown, namely, 56 days, it 
will have consumed not less than three-quarters of a pound of oak 
leaves. Thus the food taken by a single caterpillar in 56 days equals 
in weight eighty-six thousand times the original weight of the animal. 
Well might Longfellow say of the birds : 
They are the winged wardens of your farms, 
Who from the cornfields drive the insidious foe, 
And from your harvests keep a hundred harms. 
In the interests of agriculture, fruit growing, and forestry surely 
the conservation of this wild life is worthy of State attention. We 
do not simply mean the passing of an act of parliament for the pro- 
tection of certain species, but a d&ilj study of their habits and activi- 
ties and all their intricate relations to mankind. 
"But what about birds that are injurious?" If those that are 
beneficial should be protected, surely those that are injurious should 
be destroyed. Our knowledge as yet of the feeding habits of wild 
birds is so fragmentary that it would be dangerous to make the un- 
qualified statement that any species of wild bird is wholly injurious. 
Some are partly so, due in all probability to the fact that they are 
too numerous, as, for example, the house sparrow, the wood pigeon, 
the starling, etc., but there is reason to believe that if these species 
were much less numerous than at present the good they would do 
would more than compensate for any harm thej^ might inflict. It is 
therefore incumbent upon the State to walk very warily when it pro- 
ceeds to withhold protection or to frame repressive measures for the 
destruction of any species. In a like manner the granting of protec- 
tion to a bird at present generally regarded as beneficial may lead to 
an undue increase in its numbers, and within a very short time it will 
