28 FOOD OF WARBLERS 



They are even more destructive here than they ever were in 

 Europe, for here they have escaped most of their native enemies. 

 Hence those American birds that have learned to eat them may 

 prove of great economic value. It happens that the browntail 

 larvae emerge from the egg in the fall, at a time when the Warblers 

 that breed in the Canadian Provinces and the northern tier of 

 states are returning southward in migration, while the gipsy larvae 

 begin to hatch as the spring migration begins. The Warblers, in 

 both cases, appear at just the right time and destroy the small 

 larvae by thousands. The tent-caterpillar and the forest caterpillar 

 also are attacked by them during the spring, and eaten in 

 considerable numbers. The larvae of butterflies are taken as well 

 as the pupae and imagoes of many Lepidoptera. Warblers, how- 

 ever, in their selection of food are not confined to any one order 

 of insects. They are well fitted to pursue and capture any of the 

 smaller insects, except those that hide in the ground or in the solid 

 wood, and even they are in danger if they ever show themselves 

 in daylight outside their chosen retreats. 



The habits and haunts of the Warblers are so varied that, 

 collectively, the species of this family exert a repressive influence 

 on nearly all orders of insects, from those that live on or near the 

 ground to those that frequent the very tree-tops. The Oven-birds, 

 Water-Thrushes, Yellow-throats, and the other ground Warblers 

 search the ground, the fallen leaves, and undergrowth for the 

 species most commonly found there as well as those that fall from 

 the trees. Where grasshoppers are plentiful' the ground Warblers 

 sometimes feed largely on them. The bugs that are found so often 

 on berry bushes, are not overlooked, notwithstanding their rank 

 taste, which is so well known to all who have picked blueberries 

 from the bushes. The eggs of bugs are also eaten. 



Another family belonging to this order (Hemiptera), which is 

 often prominent among the food of Warblers, is the Aphididae or 

 plant-lice, previously mentioned. Most Warblers probably eat 

 certain of these insects or their eggs. Each of these eggs may 

 represent the future form of plant-louse known as the Stem Mother 

 which, no mishap occurring to shorten the natural life of her 

 descendants, would, according to Huxley, produce in ten genera- 

 tions a mass of plant-lice equal in bulk to that of five hundred million 

 human beings, or the population of the Chinese Empire. A few 

 species of Warblers eat bark lice and scale insects. 



