44 



of the spruce wonld result in (lestroyini>- the natural enemies of the 

 spruce beetle also. 



This' is, however, a problem requiring considerable knowledge of the 

 subject. Indeed, it is difficult even for one having such knowledge 

 to determine whether or not it is best to leave the matter to be taken 

 care of by friendly insects and conditions. IJndei- ordinary conditions 

 it will probably l)e as well to adopt by way of precaution one oi- moiv 

 of the simple methods snggested. 



While it may not be best in some cases to cut and remove the 

 infested trees Avhen beneficial insects al)Ound, the reverse is the case 

 when applied to the beneficial woodpeckers. 



If, as has been made clear by the abundant evidence found, the birds 

 destro}^ a large percentage of the spruce-destroying beetles in thou- 

 sands of infested trees during a single winter, it is plain that if these 

 l)irds had to confine their work to a half or a quarter as many trees, verj^ 

 few of the insects would escape. For every infested tree taken out 

 of the woods through the adoption of either of the three methods sug- 

 gested, that many less will i-emain for the l)irds to work on and con- 

 sequently fewer beetles would escape to invade the living trees. 



Previous observations by the writer, and a study of the problem of 

 the relation of birds to injurious and beneficial insects, led him to 

 believe that in the end far less service was rendei-ed by the birds than 

 was generally credited to them. This was believed to be the case 

 mainly on account of the failure of the bird to show any decided pref- 

 erence for the injui-ious over the beneficial insects. In the case of the 

 woodpeckers of the jVIaine woods, which feed on the spruce-destroying 

 beetle, however, the writer is convinced that, while the birds may, and 

 doubtless do, destroy many insect enemies of the Dendi'octonus, they 

 do far greater good than harm. It would seem, however, that the 

 relation of the birds to the beneficial insects of the northern spruce 

 forests presents some novel features wliich either do not exist or liave 

 not been noted in other sections of the country. 



The adults and larv^c of the coiiunon Clerid beetles are among the 

 most etticient insect destroyers of bark beetles. In other sections the 

 larv* of these friendly insects, as a i-ule, after they have attained 

 their full growth, go into the outer bai'k to undergo their transforma- 

 tions and to pass the winter. Here they are in especial dangei- of 

 destruction by the woodpeckers. It appears, however, that in the 

 northei-n spruce woods they have learned, possibly through the sur- 

 vival of the fittest, or the perpetuation of an acquired habit, to escape 

 the birds by going into the central tubes or tunnels in the main gal- 

 leries made by the spi-uce beetles to construct their pupa cases and 

 undergo their transformations. 



It is also pi-obable that the habit of the principal parasite of the 

 spruce beetle, which makes its cocoons in the inner bark, may enable 

 it to escape the birds. The fact, also, tluit these parasites must have 



