FOOD OF WARBLERS 27 



that in an orchard infested by canker worms, those trees nearest some 

 woods were soon cleared of the worms, mainly by Warblers, which 

 came from the woods and sprout-land to feed upon them. 



Among the favorite caterpillars eaten by Warblers are those of 

 the Tortricidae, or leaf rollers, which birds are very expert in taking 

 from their places of concealment in the rolled-up leaves. The 

 little case-bearing caterpillars, which are at times so injurious to 

 fruit, shade, and forest trees, also are eaten by Warblers. The 

 larvae of the night-flying owlet moths (Noctuidae), which include 

 the army worm and the various cutworms, are not so often eaten 

 by Warblers, but such species as climb trees are attacked by these 

 birds while the ground Warblers probably feed on cutworms to 

 some extent. 



There are some caterpillars that are supposed to have a cer- 

 tain immunity from the attacks of birds, either because they are 

 protected by spines, covered with hair, or secrete acrid or other 

 distasteful or poisonous matter which renders them unfit for food. 

 The families of silk-spinning moths, formerly collectively known 

 as the Bombycidae, but now subdivided into many groups, include 

 a number of the insects most injurious to fruit, shade, and forest 

 trees. The larvae of these insects are hairy. It is widely believed 

 that such caterpillars are never troubled by more than a very few 

 species of birds. But I have learned by observation that in these 

 cases, as in many others, protection often fails to protect. I now 

 believe that when these caterpillars are very young and small, 

 most Warblers eat them with avidity, for they can do so with 

 impunity at this time when the hairs or spines have not developed 

 sufficient strength to be disagreeable. 



The forest tent-caterpillar and the apple-tree tent-caterpillar 

 are two hairy native species, while the caterpillars of the brown- 

 tail moth and the gipsy moth, previously mentioned, are two very 

 destructive introduced species. All of these are eaten by most of 

 the commoner Warblers of New England. The two imported 

 species were fought for years by the Massachusetts State Govern- 

 ment, which expended more than a million dollars and then gave 

 up the fight. These two pests are now beyond the bounds of Mas- 

 sachusetts and may be expected to spread over a great part of the 

 United States, in spite of the fact that the fight against them has 

 now been renewed in Massachusetts and taken up in other states. 

 These insects have now become pests of the orchard, garden and 

 forest, feeding on nearly all kinds of trees and vegetation. 



