INSECT ENEMIES OF WESTERN FORESTS 155 
legs but are somewhat grublike in form. Pupation occurs within 
the larval gallery, and when about ready to change to the adult the 
pupa works partially out of the burrow, so after emergence the 
empty pupal skin is found protruding from the tunnel. 
The carpenter worm (Prionoxystus robiniae Peck) (fig. 77) is the 
most common representative of this group. It attacks oak, elm, 
poplar, cottonwood, locust, ash, maple, willow, and other ornamentals 
and also fruit trees and is distributed generally throughout the 
United States. As is the case with the carpenter moths, these moths 
cause injuries that show up later as defects in the lumber, since they 
mine in the sapwood and heartwood of trunks and limbs. It is prob- 
ably the most destructive insect enemy of oaks in California. The 
adult females are gray moths with a wing expanse of from 2 to 3 
inches. The males are smaller, with the front wings dark gray and 
the hind wings yellowish red lined with black (fig. 77). The mature 
larvae are about 214 inches in length, somewhat pinkish, with a dark 
head and with scattered hairs arising from small brown spots on the 
body. Eggs are laid in June and July, each female depositing from 
200 to 300. Three years are required to complete the life cycle. 
Another species, Acossus populi Walk., does similar work in pop- 
lars and cottonwood. Givira lotta B. and McD. works in the outer 
heavy bark at the base of ponderosa pines in Colorado. 
HORNTAILS OR WOOD WASPS 
(Siricidae) 
The horntails, or wood wasps, are injurious to the green, un- 
seasoned or moist wood of practically all western conifers. Fre- 
quently serious damage is done, especially to the wood of fire-killed 
trees. Sometimes redwood lumber is attacked and injured, even 
after it is cured and placed in storage yards. 
The adult females are thick-waisted, cylindrical wasps, with two 
pairs of wings and a hornlike ovipositor, which resembles a stinger, 
at the rear of the abdomen. They are usually of metallic colors— 
dark blue, black, or marked with orange and red. The females 
alight on freshly felled injured or dying trees and with great dex- 
terity insert their long flexible ovipositors deeply into the wood, 
often for an inch or more, and lay their eggs. Sometimes they 
are unable to extract their ovipositors from the wood and die in 
this position. The larvae which hatch from the eggs are cylin- 
drical and yellowish white, with a small spine at the posterior end 
of the body, and they sometimes hold their bodies in the shape of a 
shallow letter S. They are truly wood-eating in habit and work 
in the solid wood without any opening extending to the outside. 
As they feed they make perfectly circular holes in the wood and 
pack their boring dust in the tunnels behind them. It takes one 
or two seasons for them to complete their development. Pupal cells 
are constructed near the surface of the wood, and when the adults 
mature, they cut round, clean-cut emergence holes to the surface 
through which to escape. 
Prompt. utilization of unseasoned wood exposed to attack by 
these insects is the best means of avoiding damage. Logs placed 
in mill ponds and frequently rolled will not suffer from attacks. 
Kiln-drying gives complete control, destroying the infesting larvae, 
