The Role of Insects in the Forest* 



By JOHN B. SMITH, ScJX 



That a giant of the forest, one that has resisted the storms of 

 a century, should succumb to the attacks of an insect, countless 

 millions of which would be required to equal it in bulk, seems 

 almost absurd ; yet it is nevertheless true, though not, as a rule, 

 quite so literally as it reads. Most of our forest trees support 

 an immense insect population without showing any ill effects. 

 Nearly 500 species are known to feed on the species of oak, and 

 nearly 200 on the species of pine, in the United States. Given 

 a perfectly healthy tree, it will bring to maturity a host of 

 feeders upon its foliage, upon the smaller shoots, in the injured 

 or broken twigs or branches, in its fruit, and even in its woody 

 tissue. Comparatively few borers or other insects are able to 

 maintain themselves in the growing wood of large healthy trees, 

 and when these occur in moderate numbers they inflict only 

 such wounds as are easily healed, corresponding to mere 

 scratches in the human skin. Under some conditions these 

 insects increase abnormally, and then thousands of acres of 

 timber may be killed off. As the bleeding from many small 

 scratches may drain the human body of blood when they are 

 kept constantly open, so the boring of thousands of beetles, 

 insignificant individually, may weaken even the forest giant ; 

 and when this occurs, when there is no longer a healthy, resist- 

 ant tissue, then another host of other species steps in, adds to 

 the injury, and paves the way for yet further armies that com- 

 plete the work, leaving only a dead stick with bare branches, 

 sooner or later prostrated by a storm, and then slowly reduced 

 to dust by yet other agencies, insect, fungous, or microbic in 

 character. 



Of the feeders upon foliage in its broad sense, some, like cater- 

 pillars, feed openly and simply upon the leaf tissue, destroy and 



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