PLANT-EATING INSECTS AND MYRIAPODS 203 



One of the most striking of these is the Giant Wood- Wasp (Sirex 

 gigas) (see vol. i, p. 371), sometimes seen in this country, but 

 much more abundant on the Continent. It is of large size, some- 

 what wasp-like in appearance as the common name implies, and. 

 in the adult condition lives chiefly on honey, like most of its kind. 

 The female is distinguished by the possession of a long, straight 

 boring apparatus (ovipositor) projecting from the abdomen, and 

 often mistaken for a sting. This consists of two sheath-like 

 pieces enclosing the borer proper, made up of an upper gouge- 

 shaped piece and two firm boring rods, the ends of which are 

 beset with saw-like teeth. Besides these parts there is also a 

 strong spine projecting backwards from the tip of the body over 

 the structures just described. By means of this complicated piece 

 of apparatus the Saw- Fly bores a hole through the bark of a felled 

 or sickly fir, and lays a number of eggs in the hole so made. The 

 larvae which hatch out from the eggs resemble maggots in appear- 

 ance, and subsist upon the wood, in which they excavate galleries 

 by means of their powerful jaws, and after a variously-estimated 

 time, probably not far short of two years, pass into the quiescent 

 or pupa stage. This develops into the perfect insect, which bores 

 its way out directly to the exterior, near the place where the larva 

 entered into the pupa condition. In some species of Sirex, how- 

 ever, the quiescent stage is assumed when the larva is a con- 

 siderable distance from the surface of the trunk, so that the insect, 

 when mature, has to gnaw through a considerable thickness of 

 wood, and cases are recorded where pieces of wood containing 

 pupae have been covered with sheet-lead, and yet even this has 

 not proved hard enough to prevent the prisoners from escaping. 

 An amusing instance of late escape is mentioned in the following 

 quotation from Sharp (in The Cambridge Natural History): — 

 "After becoming full fed, the insect may still pass a prolonged 

 period in the wood before emerging as a perfect insect. As a 

 result of this it not infrequently happens that the insect emerges 

 from wood that has been carried from a distance, and used for 

 buildings or for furniture. A case is recorded in which large 

 numbers of a species of Sirex emerged in a house in this country 

 some years after it was built, to the great terror of the inhabitants. 

 The wood in this case was supposed to have been brought from 

 Canada." 



Saw- Flies proper include many species well known to culti- 



