CHAPTER II 



GALLS CAUSED BY SAW-FLIES AND GALL-WASPS 

 (HYMENOPTERA) 



THE 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. 



1. Hymenoptera SessiUventres — Insects with the abdomen 

 broad at the base, its first segment not completely amalga- 

 mated with the thorax. 



2. Hymenoptera PetioUventres 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.* 



HYMENOFTEBA SESSILIVENTBES 



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. 303. 



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