PLANT-EATING INSECTS 195 



fir tree, or one that has recently been felled, and lays her 

 eggs in the solid wood, upon which the larvae, when they 

 hatch, commence to feed. They drive long burrows 

 through the trunk, eating away the wood with their 

 powerful jaws, and passing the fragments through their 

 bodies. The wood-dust, scarcely altered in appearance 

 by the digestive process to which it has been subjected, 

 is packed tightly into the burrow behind the larva ; so 

 that the latter lives, as it were, within a cylindrical cell, 

 which is gradually moved forward as the insect continues 

 to feed. There is a good deal of conflicting evidence as 

 to the duration of the Sireos larva's life, but this is prob- 

 ably not much less than two years. Moreover, after com- 

 pleting its transformation, a considerable interval may 

 elapse before the perfect insect emerges. The full-fed 

 larva of Sir ex gigas is said to prepare the way for the 

 exit of the imago by carrying its tunnel almost to the 

 bark before changing to a pupa ; but according to Fabre 

 the European Sir ex augur pupates in the heart of the 

 trunk, and the adult insect has to cut its way through a 

 considerable thickness of wood to the surface — a task 

 which it is well able to accomplish. Instances are re- 

 corded in which these wood-wasps have actually gnawed 

 their way through a sheeting of lead with which baulks 

 of wood had been covered. Owing to their habit of 

 lying up in timber for indefinite periods, these insects 

 sometimes appear in the most unexpected places. Dr. 

 Sharp relates that "large numbers of a species of Sir ex 

 emerged in a house in this country some years after it was 

 built, to the great terror of the inhabitants. The w r ood 

 in this case was supposed to have been brought from 

 Canada." 



Besides feeding largely upon wood, insects consume 

 all manner of decaying vegetable matter. In this way 



