THE COMMON" BORER. 457 



way directly downwards in the bark, producing a 

 discoloration. If the outer, dark-colored surface 

 of the bark be scraped off with the knife the last 

 of August, so as to expose the clear white bark 

 beneath, as can easily be done without injury to the 

 tree, wherever there is a young worm it can readily 

 be detected. A blackish spot, a little larger than a 

 kernel of wheat, will be discovered wherever an egg 

 has been deposited ; and by cutting slightly into 

 the bark, the worm will be found. It gradually 

 works its way through the bark, increasing in size 

 as it advances until it reaches the sap-wood. There 

 it feeds upon the soft fibre, and forms a round, flat 

 cavity. It keeps its burrow clean by pushing its 

 excrement out of a small opening through the bark 

 at its lower end. These castings resemble fine saw- 

 dust, and enable one to detect the presence of the 

 worm. 



" When it is half grown, it seems to become con- 

 scious of the danger of its situation from wood- 

 peckers and other birds, and gnaws a cylindrical 

 retreat for itself in the solid heart-wood of the tree. 

 The excrement now, instead of being ejected, is 

 crowded into the hollow part at the bottom of the 

 cavity. This hole runs first inward and then out- 

 ward to the sap-wood, and is only covered from the 

 external air by the bark. But, as though the cast- 

 ings at the entrance were insufficient to keep out 



some marauding insect, it seems to turn itself around 



39 



