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XI. 
ON THE OCCURRENCE OF SIREX NOCTILIO AND S1REX GIGAS 
IN HERTFORDSHIRE. 
By A. E. Gibbs, E.L.S., F.E.H.S. 
Read at Watford , 3rd February , 1904. 
During the Autumn of 1903 instances of the mischief done to 
timber by the two large saw-flies Sir ex noctilio and 8. gigas were 
brought under my notice. 
In September the Instructor at the St. Albans Technical Schools, 
Mr. J. T. Baily, drew my attention to a trunk of silver-fir which 
had been purchased from a local firm of timber-dealers for use in 
the Manual Training School. It was found to be so infested by 
white, fleshy, tunnel-boring grubs, that it was quite useless for 
school purposes. I asked Mr. Baily to put the wood aside for 
observation, and in a few days a female specimen of Sir ex noctilio 
emerged, and this was succeeded by the appearance of a number of 
other specimens, the emergences continuing at intervals until the 
advent of the cold weather. As the insects left the galleries in 
the wood they flew to light, and were mostly captured on the 
window-panes, and sometimes three or four were buzzing about at 
the same time. The galleries excavated in the wood by the grubs 
ran in all directions; indeed, the tree was completely riddled by 
them. Enquiries elicited the fact that the silver-fir was grown on 
the Bussells Estate, the property of Mr. Lewis Evans. 
Sir ex noctilio is the smaller of the two species of giant saw-flies, 
or tailed wasps as they are often called, which occur in sufficient 
numbers in this country to he regarded as British insects. 
The genus Sirex belongs to the Siricidae, one of the two families 
into which the phytophagous or vegetable-feeding Hymenoptera 
are divided. This family can he at once identified by the long 
powerful ovipositor of the female, which is adapted for piercing 
the hark of trees in order to deposit the egg in the wood in which 
the larvae feed. I may he pardoned for reminding you that the 
order Hymenoptera is primarily divided into two groups, the 
Terehrantia or Borers, of which we have a good example in 
the species under notice, and the Aculeata or Stingers, to which 
the bees and wasps belong. 
The insect with which we have now more particularly to deal is 
generally known as the steel-blue or “ common ”/ saw-fly, though 
it does not appear to be very abundant in England and is certainly 
rare in this county. The female has a handsome purple-blue 
abdomen, terminated by a spike-like projection, which is the ovi¬ 
positor. The male is a different-looking insect, the abdomen being 
yellow with a black apex. The eggs having been deposited in 
a suitable tree by the female, they in due course hatch, and the 
young larvae commence to bore galleries in the solid wood. They 
are fleshy, cylindrical grubs, with strong mandibles, without eyes, 
