TENTHREDINIDJE, OR SAW-FLIES. SIRICID.E. 161 



more, a whole field has been often devastated by the voracity of 

 the larvae, which devour the soft tissue of the leaves, leaving only 

 their skeletons and stalks. The most effectual remedy for these 

 attacks was found to be the introduction of Ducks into the fields, 

 by which the plants were cleared of the larvae more effectually 

 than they could be by any other means. Many other species 

 exist, however, almost equally injurious to different tribes of 

 plants. Thus the Gooseberry is subject to the attacks of a 

 Tenthredo, of which the larvse often amounting to as many as 

 one thousand upon a single tree devour its leaves at the begin- 

 ning of summer. The Apple, again, suffers from the deposition 

 of the eggs of another species in its fruit. And the Willow is 

 subject to the attacks of many species, some of which devour its 

 leaves, whilst others cause the production of galls by perforating 

 its branches. The perfect Insects of this group are of moderate 

 size, not exceeding an inch in length ; some of them, however, 

 are among the largest Hymenoptera inhabiting this country. 

 Their flight is usually heavy, and is attended in the larger 

 species with a humming noise ; it seems, however, to be more 

 agile in the hot sunshine. They come forth for the most part in 

 the spring, having passed the winter in the pupa state ; and they 

 usually obtain their chief supply of food from the pollen or honey 

 of flowers, especially those of the Umbelliferous tribe ; some of 

 them, however, attack and devour living insects which frequent 

 the same plants. The ravages of these insects are restrained 

 by the destruction of vast multitudes of their larvae, through the 

 agency of the Entomophagous, or parasitic section of this group ; 

 thus the Lophyrus pini, a Saw-fly which infests the Pine, is 

 itself subject to the attacks of at least twenty parasites, of which 

 fifteen are Ichneumonidae. 



688. The SIRICID^E bear a strong general resemblance to the 

 preceding group, both in structure and habits ; but they have a 

 stronger ovipositor, which enables them to pierce not merely the 

 soft substance of trees or young shoots, but hard timber. 

 The larvae produced from the eggs thus deposited, usually reside 

 in the interior of trees, which they perforate in various directions; 

 often causing great destruction of the Pine forests, of which the 



