4 68 



Saw-flies, Gall-flies, Ichneumons, 



Cynipid gall-flies. These flies (Fig. 655) are all very small, the largest 



species not being more than inch long; 

 they are short-bodied and have in most 

 cases four clear wings with few veins. 

 The females and in numerous species 

 there seem to be no males have a long, 

 slender, and flexible but strong, sharp- 

 pointed ovipositor (Fig. 656), composed of 

 several needle- or awl-like pieces, which 

 is used to prick (pierce) the soft tissue of 

 leaf or tender twig so that an egg may be 

 deposited in this succulent growing plant- 

 tissue. 



Each female thus inserts into leaves or 

 twigs many eggs, perhaps but two or three 

 in one leaf or stem if the galls are going 

 to be large ones, or perhaps a score or so if 

 the galls will be so small as to draw but little on the plant-stores and 

 be capable of crowding. In two or three weeks the egg gives birth to 

 a tiny footless maggot-like white larva which feeds, undoubtedly largely 

 through the skin, on the sap abundantly flowing to the growing tissue in 

 which it lies. With the birth of the larva begins the development of the 



FlG. 655. A gall-fly, species unde- 

 termined. (Much enlarged.) 



FlG. 656. Ovipositor of a gall-fly, dorsal and lateral views; the long tapering part is 

 the piercing portion; the other parts constitute levers and supports (After Lacaze- 

 Duthiers; greatly magnified.) 



gall, which is an abnormal or hypertrophied growth of tissue about the point 

 at which the larva lies. The excitation or stimulus for the growth undoubtedly 

 comes from the larva and probably consists of irritating special salivary 

 excretions and perhaps also of physical irritation caused by the presence 



