248 USEFUL BIRDS. 



species that infest live trees are found during a part or all of 

 their lives just under the bark or in the sap-wood not very 

 far from the surface ; and the Woodpecker can drill a small 

 hole into the burrow, insert its open beak, and 

 with its tongue spear and extract the insect. 

 The wound soon heals, leaving no noticeable 

 trace. A Woodpecker may thus reach insects 

 at a depth of from one to four inches, accord- 

 ing to the size of the bird. Dead trees, how- 

 ever, are riddled with borers in all their parts, 

 Fi 106 — pues ^^^^ ^^^^ birds are obliged to delve deeply to 

 weevil, a destruc find them ; therefore, the work of the birds 



tive pine insect, . i i . • i i 



eaten by Wood- lu dead trces IS most noticcable. 



peckers. -j^j^^ cliief valuc of the Woodpeckers con- 



sists in the fact that Avhen they find a tree infested with bor- 

 ers they are likely to keep at work upon it until no more 

 larvse can be found. Thus they often save the tree, and 

 check an incipient outbreak of borers. Woodpeckers so en- 

 gaged sometimes destroy parasites of boring insects. Such 

 destruction of useful insects by these birds is of little conse- 

 quence ; for when the birds destroy the grubs, the parasites 

 are not needed. When the birds are too few in numbers to 

 prevent an increase of boring insects, the parasites also have 

 a similar immunity from the attacks of birds, and so are free 

 to exert their influence in restraining the borers. If Wood- 

 peckers should eat an undue number of parasites, they might 

 then be doing harm ; but such cases probably seldom occur. 

 The Woodpeckers are also useful in providing homes for 

 other birds. Most Woodpeckers each year hollow out from 

 the wood a home for their young, and rarely, if ever, use it 

 more than one season. Some species, of which the Downy 

 and the Hairy Woodpeckers are familiar examples, also 

 excavate holes to which they retire for shelter during winter 

 nights. The larger Woodpeckers often make deep holes in 

 dead trees while digging out large borers or colonies of ants. 

 When the carpenter birds are through with these cavities 

 they are sometimes used as nesting places by other birds 

 that are unable to excavate for themselves. The deserted 

 nests of the Downy Woodpecker are used by the Wren, the 



