188 HOMES WITHOUT HANDS. 



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

 the observer will 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 gradual- 

 ly increase to their termination. The cause of this formation is 

 as follows : 



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

 rows 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 outward. 



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

 arrangement becomes evident. As they increase in size, the bur- 

 rows 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 keeping pace 

 with their increasing size. It will easily be seen by reference to 

 the illustration, that if a number of these beetles attack a tree, the 

 bark is gradually separated from the woody portion, and that, as 

 in all exogeneous trees the nourishment is derived from the bark, 

 the tree must die as soon as the functions of the bark are sus- 

 pended. 



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 supply 

 of nourishment. The tree is thus starved to death, and in the 

 following year, a fire applied to the trunk is able to burn it 

 through, and bring down the tree with scarcely any expenditure 

 of labor by the settlers. This mode of killing a tree is technical- 

 ly called "girdling" it. In proportion, therefore, to the amount 

 of bark removed, the tree sickens, from defective nourishment, 



