DAMAGE CAUSED BY ANIMALS. 189 



B. WOOD-WASPS (Siricidtz or Uroceridte). 

 90. Wood-wasps, Siricidte. 



The wood- wasps belong to the class of technically injurious 

 insects, as their large larvae often render timber unfit for many 

 technical purposes by boring deeply into the wood. They only 

 attack coniferous timber. 



By means of a long ovi-depositor the female wasp lays her 

 eggs singly in the wood of the stem, principally selecting trees 

 that have become sickly in growth in consequence of overtapping 

 for resin, stripping of the bark by red-deer, injury by lightning, 

 or other external injuries, whilst decidedly avoiding rotten wood. 

 The larva bores first of all in the softer sapwood, but gradually, 

 with growing strength, works deeper into the stem, and in the 

 spring following the second winter again bores its way towards 

 the surface of the trunk for the purpose of forming a pupal 

 chamber in the sapwood. About the middle of summer the 

 fully-developed wasp bores a round hole straight through to the 

 surface, and issues for the purpose of swarming and reproduction. 

 The galleries bored in the wood by the white, cylindrical, thick 

 larvae, which have a short terminal borer pointing upwards, are 

 also circular. 



Their generation is always biennial at least, and sometimes 

 longer, for occasionally the wasps make their appearance from 

 beams and scantlings that have been prepared and worked up for 

 some length of time. 



The three chief species are : 



The Pine Wood-wasp, Sirex juvencus, which occurs almost 

 entirely in Pine timber. The female has a steel-blue body, whilst 

 the male is usually much smaller in size, and of a yellowish- 

 red colour from the third to the seventh sections of the abdomen. 



The Giant or Yellow Spruce Wood-wasp, Sirex gigas ( Vide Plate 

 IY. fig. 22), which inhabits Spruce and Silver Fir. It is of a 

 blackish colour, with a yellow patch behind the eyes. In the 

 female the two first and the three last sections of the abdomen 

 are yellow, whilst in the male all the rings are reddish-yellow, 

 with the exception of the first and the last, which are black. 



The Black Spruce Wood-wasp, Sirex spectrum, also inhabiting 

 Spruce and Silver Fir, and of a bluish-black colour, with yellow- 



