CHAPTER II 
GALLS CAUSED BY SAW-FLIES AND GALL-WASPS 
(HYMENOPTERA) 
T HE order Hymenoptera includes ants, bees, wasps, 
saw-flies, and ichneumon-flies, insects which easily 
take the first place as regards intelligence. It is divided 
into two very distinct sub-orders. 
i. Hymenoptera Sessiliventres —Insects with the abdomen 
broad at the base, its first segment not completely amalga¬ 
mated with the thorax. 
2. Hymenoptera Petioliventres or Petiolata —The abdomen 
connected with what appears to be the thorax by a slender 
joint, the posterior part of the apparent thorax consisting of 
an abdominal segment.* 
HYMENOPTERA SESSILIVENTRES 
This suborder is divided into four families. The larvae 
of the majority usually destroy leaves after the manner of 
caterpillars, but in one family, the Tenthredinidae or saw- 
flies, the larvae of a few species live in galls. 
Saw-flies are sluggish insects, chiefly occurring in May, 
June, and the early part of July. The second brood appears 
at the end of July and throughout August. The eggs are 
placed in the plant by a special apparatus, the ovipositor, 
or saw. This wonderful instrument has received the 
admiration of naturalists from the early days of entomology. 
Two centuries ago Reaumur described the saw, and also 
commented upon the placid disposition of saw-flies, suggest- 
* Sharp, "Insects,” in “Cambridge Natural History” vol. i., 
P. 5 ° 3 - 
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