UTILITY OF BIRDS IN NATURE. 17 
do not neglect any one element of their ordinary food in 
such cases. They neglect them all, both animal and vegetal, 
for the time being, and turn to the now abundant insect food 
that is more readily accessible. This I have observed in 
studying outbreaks of cankerworms, and Professor Forbes 
records a similar experience with birds feeding on canker- 
worms.! , 
This apparently agrees with the experience of the forest 
authorities in Bavaria during the great and destructive out- 
break of the nun moth (Liparis monacha) which occurred 
there from 1889 to 1891. The flight of Starlings collected 
in one locality alone was credibly estimated at ten thousand, 
all busily feeding on the caterpillars, pups, and moths. 
Enormous flights of Titmice and Finches were similarly 
engaged. The attraction of Starlings to such centers be- 
came so great that market gardeners at a distance felt their 
absence seriously.? 
Evidently in such cases the birds, changing their usual 
fare entirely for the time being, remove their restraining 
influence from both useful and injurious insects, leaving one 
to exert its full force as a check on the other, until the urgent 
business of the serious outbreak of grasshoppers, caterpillars, 
or some other pest has been attended to; then the birds 
return to their usual haunts and food, and exert the same 
repressive influence as before. 
Although the insects which are potentially injurious are 
greatly in the majority, there are many species which per- 
form a very apparent useful function in nature. Such are 
the bees and some of their allies of the order Hymenop- 
tera, — insects which travel from flower to flower in search 
of sweets, and, becoming loaded with pollen, fertilize the 
blossoms, rendering the trees fruitful. Other insects seem 
especially adapted to hold the potentially injurious species 
in check. Some which are called predaceous insects attack 
other insects and devour them, as do the ground beetles 
+ The Regulative Action of Birds upon Insect Oscillations, by S. A. Forbes. 
Bulletin No. 6, Illinois State Laboratory of Natural History, 1883, p. 21. 
2 Protection of Woodlands, by Herman Fiirst. English edition, translated by 
John Nisbet, 1893, p. 126, 
