39 



Birds materially restrict the Increase ok Hairy Caterpillars. 



The writer has earnestly endeavored to determine to what extent birds 

 control the increase of hairy caterpillars. The result of the investiga- 

 tion is not as yet conclusive, but much can be deduced from the array of 

 facts presented. 



It is certain that many birds prefer smooth-skinned caterpillars, 

 Many species have uot been observed to eat hairy caterpillars at all, 

 while it is safe to say that most land birds feed readily upon smooth- 

 skinned caterpillars. Take for example the larva? of the canker-worm 

 moths, Paleacrita vernata and Anisopteryx pometaria. Nearly al 1 species 

 of birds in eastern Massachusetts, from the titmouse to the crow, have 

 been observed to feed upon these larva?, and when these are abundant 

 most birds seem to prefer them to the hairy caterpillars. The tent cat- 

 erpillars, hatching as they do very early in the season, form when small 

 a staple food for a great number of birds. Later, as the canker worms 

 appear and the tent caterpillars grow larger and, presumably, more dis- 

 agreeable to some birds, they are neglected to some degree, While most 

 birds feed on the canker worms. When the canker worms disappear 

 many birds again resume feeding on hairy caterpillars. The presence 

 of a quantity of smooth-skinned caterpillars, therefore, usually benefits 

 the hairy caterpillars. 



Every one who has studied carefully the life history of moths lias 

 been struck with the great mortality among the young larva?. In a 

 study of the natural increase of the gypsy moth it was found that 

 where a single egg cluster hatched isolated from its kind most of the 

 caterpillars disappeared while they were quite small ; in some cases the 

 entire brood was destroyed. 



It is well known that the gypsy moth in Massachusetts has few effec- 

 tive natural enemies except the birds. Birds frequently have been 

 observed feeding upon the young caterpillars, and careful observa- 

 tion indicates that many of them are destroyed by birds before they 

 are half grown. Two instances have been reported where small but 

 flourishing colonies of gypsy caterpillars appear to have been exter- 

 minated by birds. Limited outbreaks of the brown-tail moth that 

 have been watched have been so reduced that at the end of the season 

 few or none could be found. Just what proportion of this destruction 

 is due to the parasites and other enemies of the brown-tail moth it is 

 diffiult to determine, but the observers are agreed that most of it is due 

 to birds. In some cases the webs of the tent caterpillar are torn open 

 by birds and all or nearly all of the caterpillars in the webs destroyed. 



The most striking instance observed of the check exerted by birds 

 on the increase of hairy caterpillars was in Georgetown, Mass., in July, 

 1899. Here a colony of the gypsy moth had grown and flourished in 

 the woods unknown to any one until it was discovered in midsummer. 

 The moths had been increasing there without any check, excepting their 

 natural enemies, and they had defoliated the trees and shrubbery on 

 at least two acres of land, stripping both pine and hard-wood trees. 

 A vast swarm of caterpillars had been at work there. It was 

 noticeable, however, that the caterpillars were not nearly so numerous 

 at the time of their discovery as had been the case in other localities 

 where they had not clone so much injury. In other words, there were 

 not enough caterpillars to account for the destruction of the foliage. 

 The colony was near the edge of the woods, with a field and meadow 

 on one side and an orchard near by. Birds abounded in the vicinity. 

 So soon as one came within hearing distance of the place cries of crows 

 and blue jays were heard in and about the edges of the stripped tract. 

 Many chickadees, tanagers, thrushes, warblers, sparrows, flycatchers and 

 cuckoos were about. At the foot of some of the large trees hundreds of 

 dead and dying caterpillars were found which evidently had been injured 



