44 



of the spruce would result in destroying 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. Under ordinary conditions 

 it will probably be as well to adopt by way of precaution one or more 

 of the simple methods suggested. 



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

 infested trees when beneficial insects abound, the reverse is the case 

 when applied to the beneficial woodpeckers. 



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

 destroy a large percentage of the spruce-destroying beetles in thou- 

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

 birds had to confine their work to a half or a quarter as many trees, very 

 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 remain for the birds 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 rendered 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 injurious over the beneficial insects. In the case of the 

 woodpeckers of the Maine 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 Dendroetonus, 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 which either do not exist or have 

 not been noted in other sections of the country. 



The adults and larvae of the common Clerid beetles are among the 

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

 larva* of these friendly insects, as a rule, after they have attained 

 their full growth, go into the outer bark to undergo their transforma- 

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

 destruction by the woodpeckers. It appeal's, however, that in the 

 northern 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 spruce beetles to construct their pupa cases and 

 undergo their transformations. 



It is also probable 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, thai these parasites must have 



