586 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
Surerramity SJ/RICOIDEA 
The Horntails, or Wood Wasps 
The adults of the superfamily Siricoidea are commonly called horn- 
tails or wood wasps because the end of the abdomen terminates in a 
spine or horn directed backward and somewhat upward, and also 
because many resemble wasps. They are closely related to the saw- 
flies but differ from them by the fact that the abdomen of the female 
is furnished at the tip with a rather long drill or boring apparatus, 
instead of the sawlike plates. They further differ in the habits of the 
larvae, which are borers in solid wood. The feniale drills a deep hole 
into a tree and deposits an egg in the bottom of it. Sometimes the 
boring apparatus becomes caught in the wood, and the female remains 
a captive until she dies. The larvae are cylindrical and eyeless, and 
have three pairs of fleshy, unjointed, and poorly formed thoracic legs 
and no abdominal prolegs. 
Both deciduous and evergreen trees are infested by the various 
species of horntails. The larval galleries through the wood are cylin- 
drical and tightly packed with fine boring dust. The horntails gen- 
erally attack trees or portions of trees that are dead or in a badly 
weakened condition. A few species, however, have been reported as 
attacking trees in a vigorous condition. Transformation to the adult 
stage takes place in the burrows or galleries, and the holes through 
which the adults emerge are circular in outline. 
FIGURE 171. 
Female of the parasite Megarhyssa lunator ovipositing in a tree 
] g 1 I s 
infested with horntails. 
