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, 
Fig. 106.—Pates 20d the birds are obliged to delve deeply to 
weevil,adestruc- find them; therefore, the work of the birds 
tive pine insect, , e ‘ 
eaten by Wood. in dead trees is most noticeable. 
Deckers. The chief value of the Woodpeckers ‘con- 
sists in the fact that when they find a tree infested with bor- 
ers they are likely to keep at work upon it until no more 
larvee 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 Dowty Woodpecker are used by the Wren, the 
