148 PROTECTION AGAINST BIRDS. 



this manner more or less throughout the year, the former 

 chiefly on trees, and the latter more on the surface of the 

 ground. 



Woodpeckers detect insects by the senses of sight, smell and 

 sound; it is not yet decided which of these is predominant. It 

 cannot be denied that they prefer the large but less harmful 

 larvae of Ceranibycidae, Cossus and Sirex, to the minute larvae 

 of weevils and bark-beetles, but repeated observation shows 

 that they are also keen hunters of the latter. Amongst the 

 most hurtful species which they destroy may be mentioned 

 Pissodes pini, L., P. notatus, Fabr., Myelopliilns piniperda, L., 

 and Hylastes palliatus, Gyll. The damage done by the black 

 and ground woodpeckers to ant-hills may indeed be classed as 

 injury to the forests, to which ants are useful, but living larvae 

 of parasitic beetles are, when present, often preferred to ants 

 by the woodpeckers. 



1. Nidification in Trees. 



Woodpeckers cannot make nest-holes in trees without 

 injuring them, but this is done chiefly in the case of soft- 

 wooded species, the aspen, lime, etc., or in rotten old hard- 

 woods. The damage done is not great, and the holes are 

 subsequently used for breeding by several useful birds, 

 starlings, titmice, and flycatchers, the former frequently 

 driving the woodpeckers from a new hole they have just made, 

 in order to build their own nest there. 



5. Summary. 



The result of investigations into the utility of woodpeckers 

 tends to show that these birds by their activity in the destruc- 

 tion of insects play a most useful part in Nature, and should 

 therefore be protected by foresters. Hess holds the same 

 views as Borggreve, that all useful birds tend to prevent an 

 undue preponderance of insects, keeping their numbers more 

 or less normal in ordinary years. In case of a great insect 

 calamity, however, the action of birds is inadequate to protect 

 the forests ; ichneumon-flies and fungoid diseases eventually 

 put a stop to the plague. 



