THE SAWFLY GROUP 



297; 



THE SAWFLY GROUP SUBORDER Sessiliventres 



This group contains the various species of sawflies, and may be subdivided into 

 the sawflies proper (Tenthredinidtz} and the wood borers, or tailed wasps {Siritida), 

 although it also comprises the little pith-boring Cephida and the rare and little- 

 known species of Oryssidce. The food of the larvae of these insects consists entirely 

 of vegetable matter. In the case of the first-named family, the leaves of trees and 

 shrubs; in that of the second, the solid wood of various trees; and in the case of the 

 third, the tender pith of the stalks of rye and also the shoots of pear and other trees. 

 Such grubs as are internal feeders are either limbless, or have at most six more or 

 less rudimental thoracic legs. Those, on the other hand, which live a free life and 

 feed on foliage, are very similar in general appearance to lepidopterous larvae, from 



1. Sirex juvencu s, female larva, pupa (all of natural size); 2. CORN SAWFLY and larvae in the rye stalks; 

 3. Pachymerus calcitralor, a wasp parasitic on the above; 4. Larva and pupa of Cephus (enlarged). 



which they may be distinguished by the greater number of their legs; these varying 

 from twenty to twenty-two, whereas those of the Lepidoptera have but sixteen at 

 most. They also differ by the shining and almost naked skin, and the curious habit 

 possessed by many of curling in the posterior segments, raising them at the same 

 time and depressing them with a rhythmic movement. This action, which may be 

 for the purpose of frightening away foes, coupled with the melancholy-looking eyes, 

 gives them a grotesque appearance, not observable in the caterpillars of the 

 Lepidoptera, save in a few instances. When full grown, the majority of the larvae 

 leave the food plant and spin in or on the surface of the ground, or under dry leaves 

 and moss, a barrel-shaped cocoon in which they pass the winter, turning to a 

 chrysalis only a short time before the perfect insect emerges. At least a thousand 

 species are known, though this is probably but a small moiety of those that exist. 

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