SCOLYTUS. 169 



to insects. The pleasure of the discovery nearly compensated for 

 the disappointment concerning the shot, the possession of which 

 seemed to my boyish mind to be a manly trait of character, and 

 calculated to raise me in the eyes of my playfellows. 



If the bark be cut through, and then raised with the knife, the 

 curious radiating system of tunnels will be exposed to view, and 

 the observer wiU notice that, however these tunnels may vary 

 in size and direction, they all agree in these points ; firstly, that 

 they radiate nearly at right angles from a single cylindrical 

 tunnel ; and secondly, that they are very small at their base, and 

 gradually increase to their termination. The cause of this forma- 

 tion is as follows : — 



The mother insect enters the bark in search of food, and 

 burrows deeply into the tree, sometimes boring into the substance 

 of the wood itself, but generally cutting a tunnel between the 

 wood and the bark. She then deposits her eggs regularly along 

 the cylindrical tunnels, and in most cases retreats to the entrance, 

 and there dies, her body forming a natural stopper. In due time 

 the eggs are hatched, producing a number of very minute white 

 grubs, which immediately begin to feed, the substance of the 

 tree being the only diet of this insect in every stage of existence. 

 Urged by a wonderful instinct, each grub arranges its body at a 

 right angle with the burrow in which it was hatched, and so eats 

 its way steadily outwards. 



When the grubs have made some progress, the wisdom of this 

 arrangement becomes evident. As they increase in size, the 

 burrows necessarily increase with them, so that if they had all 

 started parallel with each other, the tunnels would coalesce and 

 the grubs be unable to procure their proper amount of food. As 

 however, the tunnels radiate like the spokes of a wheel, they very 

 seldom interfere with each other, their radiation more than keep- 

 ing pace with their increasing size. It will easily be seen by 

 reference to the illustration, that if a nvimber of these beetles 

 attack a tree, the bark is gradually separated from the woody 

 portion, and that, as in aU exogenous trees the noxirishment is 

 derived from the bark, the tree must die as soon as the functions 

 of the bark are suspended. 



Settlers in any new colony are well aware of this fact, and 

 when they want to kill a tree, they do so by simply removing a 

 rather wide ring of bark from the trunk, and thus cutting off the 



