IN HERTFORDSHIRE. 
75 
informed me that quite a number of them, of both sexes, had 
appeared in the same place. Investigation showed that they were 
emerging from a heap of fir-wood which had been cut up for fuel. 
The tree grew in Mr. Kitton’s garden, and as it was left upon the 
ground for some time before it was cut up, the probability is that 
the eggs were then deposited in it. A . piece of the wood, badly 
tunnelled by the grubs and the escaping flies, was kindly sent to 
me by Mr. Kitton, and I am utilizing it, and also the wood 
damaged by S. noctilio , in making up a case for the County 
Museum, to show the destruction that may he done to timber by 
these insects. 
a b 
Fig. 22. —Sirex gigas. a , male ; b, small female ; c, female of normal size. 
Seven-eighths natural size. 
Sirex gigas is a larger, and, so far as my experience goes, 
a commoner species than S. noctilio. In the female the base and 
apical segments of the abdomen are yellow, and the central 
segments black, giving the insect a hornet-like appearance. The 
ovipositor is longer than in the first-mentioned species. The male 
is very similar to the male of S. noctilio , but may he at once 
distinguished by its yellow antennse. As will he seen from the 
illustration (Fig. 22, b, c), the females of this species vary very 
greatly in size. The late Miss Ormerod expressed the opinion 
that this variation is influenced by the conditions of the maggots 
having been favourable or otherwise, instancing some females 
of large size sent to her from an old silver-fir where every¬ 
thing must have been suitable for growth, as compared with 
