194 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY, 
bark, and then taking the larvee or pupe found on the outside of 
the wood. Curiously enough, where the bark is thick and the 
larve and pupe are contained therein, the squirrel remains 
ignorant of the fact, and passes these over. As bearing out my 
advice last year in my notes on the squirrel, Mr Clark, after men- 
tioning the grub-destruction by the squirrel, hastens to add, 
“ squirrels, however, must be kept under, for I have taken from a 
wood over ten thousand fir trees killed by squirrel.” 
Specimens of the Steel-blue Wood-Wasp (Sivrex juvencus) were 
sent from Dunraven, and the borings of the Giant Wood-Wasp 
from Aberdeen, so a note on these two pests may be timely. 
DESCRIPTION OF INSECTS. 
Sirex gigas, the Giant Wood-Wasp.—This insect varies much 
in size, from over half an inch to one inch and a half. The 
smaller male has all the rings of the abdomen reddish-yellow, 
except the first and the last, which are black. The female has 
the first two and the last three segments of the abdomen yellow, 
and the rest black. 
Spruce and silver fir,and sometimes larch and pine, are attacked 
by this species, old timber being preferred. 
Sirex juvencus, the Steel-blue Wood-Wasp.—Here also the 
males are smaller, and the colour varies. The females are blue, 
while abdominal rings 4 to 7 of the male are yellowish-red. 
Pine, in the pole stage, is chiefly resorted to by this species, but 
there are also recorded attacks on spruce and silver fir. 
These two species of Hymenopterous insects are not uncommon 
in Britain, and imported coniferous timber often harbours them. 
It is the larval stage which is injurious, the tunnels made in solid 
timber by the larvze often rendering the timber useless for technical 
purposes. The mature insects are large and striking, and, from 
the humming noise of their flight, invite attention. 
The life-history is as follows:—The female, by means of a long 
and strong ovipositor, bores a hole through the bark into the 
alburnum or sap-wood of standing sickly trees or on blown or felled 
timber. This she does very quickly. One egg is deposited in 
each such boring. From the egg hatches out a grub, which when 
full grown measures over an inch in length. It is cylindrical 
and whitish, with three small pairs of thoracic feet, and strong 
biting jaws. A spine on the last segment is very characteristic. 
