INTRODUCTION. 9 



is done to the tree by these voracious beings. The process up to a 

 certain limit may be one of natural and healthy pruning, but there is 

 no certainty that the limit may not at any time be overstepped and 

 destruction ensue. The tree is attacked in a multitude of ways by cater- 

 pillars alone. The buds are eaten by various leaf-rollers (Tortrices), 

 the leaves are mined on the upper and under sides by various Tineids, 

 while the leaves are rolled over in various ways and in various degrees 

 to make shelter for the caterpillars, or they are folded on the edges, or 

 gathered and sewed together by Tineid, Tortricid, and Pyralid larvae. 

 The entire leaves are devoured by multitudes of species of larger cater- 

 pillars, belonging especially to the Pyralid, Geometrid, Bombycid, and 

 Sphingid moths ; while certain species prey on the fruit, acorns, nuts, 

 and seeds. 



It is a singular fact that of the great family of Owlet or Noctuid 

 moths, of which there are known to be 1,200 species in this country, 

 very few feed on trees, the bulk of them occurring on herbaceous plants 

 and grasses. 



While the smaller caterpillars (Microlepidoptera) feed concealed 

 between the leaves or in the rolls or folds in the leaf, or in the buds, the 

 caterpillars of the larger species feed exposed on or among the leaves. 

 Here they are subject to the attacks of birds and of Ichneumon and 

 Tachina flies, which are constantly on the watch for them. And it is 

 curious to see how nature has protected the caterpillars from observa- 

 tion. While the young of the smaller moths are usually green and of 

 the same hue as the leaves among which they hide, or reddish and 

 brownish if in spruce and fir buds, where they hide at the base of the 

 needles next to the reddish or brownish shoots, the larger kinds are 

 variously colored and assimilated to those of the leaves and twigs 

 among which they feed. Were it not for this they would be snapped 

 up by birds. Of course, the birds devour a good many, and the pry- 

 ing Ichneumons and Tachinae lay their eggs in a large proportion, but 

 those which do survive owe their safety to their protective coloration. 



Of some twenty or more different species of Geometrid caterpillars 

 which occur on the evergreen trees, some are green and so striped with 

 white that when at rest stretched along a pine needle, they could with 

 diflBculty be detected; others resemble in various ways (being brown 

 autl warted) the small twigs of these trees ; and one is like a dead red leaf 

 of the fir or hemlock. There are several span-worms on the oak, which 

 in color and markings, as well as in the tubercles and warts on the body, 

 resemble the lighter or darker, larger or smaller knotty twigs; this 

 resemblance, of course, is in keeping with the characteristic habit of 

 these worms of holding themselves out stiff and motionless when not 

 feeding. 



In an entirely different way the various kinds of N'otodontian cater- 

 pillars, which feed exposed on oak leaves, are protected from observa- 

 tion. They feed on the edges of the leaves, and their bodies are green^ 



