100 



Wood Wasps. 



[may, 



insects. The head and body are black except the first two and 

 the last three segments of the abdomen, which are yellow. The 

 head behind each eye is yellowish. The shanks and the feet are 

 yellow. The abdomen ends in a spine below which is the con- 

 spicuous ovipositor. The four membranous wings are brownish- 

 yellow. The male is smaller, reaching i|- in. in length, though it 

 may measure less than an inch. It is distinguished further from 

 the female by its abdomen being red or reddish-yellow, except 

 the first and the last segments, which are black or dark brown. 

 Sir ex gigas lays its eggs typically on spruce, but also on silver 

 fir and more rarely on pine and larch. 



Sirex juvencus. — The female may measure — including the 

 ovipositor — up to i\ in., but may be less than an inch. It is 

 steel-blue in colour with reddish or reddish-yellow legs. The 

 wings are clouded with yellow. The male may measure up to 

 i£ in. Measurements of specimens taken by me in the same 

 year are £ in., f- in., i in., t\ in. Rings 4 to 7 of the abdomen 

 are red or reddish-yellow. In Sirex juvencus the head behind 

 the eyes has not the yellow spots characteristic of Sirex gigas. 

 Sirex juvencus lays its eggs typically on pine, but also some- 

 times on spruce ; occasionally eggs are laid on silver fir. 



Sirex grubs are round and whitish. The head, provided with 

 horny jaws, is followed by twelve segments. The three seg- 

 ments behind the head each bear a pair of weak legs ; there are 

 slight fleshy prominences on the other segments, but no legs ; 

 the hind segment ends in a horny spine. On each side of the 

 grub are ten stigmata. 



Life-history. — The female, by means of the ovipositor, bores 

 through the bark of the tree right into the outermost youngest 

 wood ring, and in each boring lays an egg. The larva on 

 hatching may gnaw in the same wood-layer for a time, but later 

 eats its way towards the centre of the stem. It afterwards 

 curves round and gnaws its way towards the periphery, so that 

 the completed tunnel or boring is more or less circular or sickle- 

 shaped. This tunnelling outwards again to the outside of 

 the wood has the advantage of leaving the adult insect, after 

 pupation, with not too great a thickness of wood to eat through 

 on its way to the open air. The tunnels are round in section 

 and show plentiful frass and bore-meal. The full-fed grub 

 pupates towards the end of its tunnel, and the adult insect, when 



