204 



THE FOOD OF ANIMALS 



SA 



Fig. 438. Hinder end of a Saw-Fly 

 (greatly enlarged), 

 ture. 



vators from the ravages committed by their larvae on the leaves 

 of various plants. One of the commonest of these is the Turnip 

 Saw-Fly (Athalia spinarum) (see vol. i, p. 371), which often 

 inflicts serious damage upon the leaves of the crop after which 

 it is named. The females of this and other species are provided 

 with a complex ovipositor placed near the hind end of the body, 

 and constructed on somewhat the same lines as the corresponding 

 organ of the Giant Wood- Wasp described above. It consists (fig. 

 438) of two elegantly-curved saws, each of which can be worked 



backwards and forwards along a groove 

 in a directing piece, and when not in 

 use is protected by a sheath. The saws 

 have elaborately -toothed edges, and 

 their outer surfaces are ribbed so as to 

 confer a power of rasping. When in 

 use they are protruded from their sheaths 

 LAP. intestinal aper- an( j worked alternately, so as to make 

 an incision, within which an egg is then 

 deposited. The larvae which issue from these eggs somewhat 

 resemble the caterpillars characteristic of moths and butterflies, but 

 differ in certain particulars, as, for example, the presence of more 



numerous pro-legs than in 

 caterpillars properly so called. 

 The remaining species of 

 the Hymenoptera are char- 

 acterized by the possession of 

 a " waist", and they include 

 many plant-feeding insects, 

 such as most gall-flies, all 

 bees, and certain sorts of 

 wasps and ants. 



GALL-FLIES are small or 

 very small insects which are 

 mostly responsible for those 

 curious excrescences upon 

 plants to which the term 

 "gall" is popularly applied. 

 Oaks are especially prolific in these structures, and the tufted red 

 swellings common upon roses, and known as bedeguars, furnish a 

 familiar example of them. The Rose Gall- Fly (Rhodiies rosce) (fig. 



Fig. 439. Rose Gall-Fly (Rhodites rosce] and Bedeguars. 

 Actual size of insect indicated by the crossed lines. 



