468 



Saw-flies, Gall-flies, Ichneumons, 



Cynipid gall-flies. These flies 



Fig. 655. — A gall-fly, species unde- 

 termined. (Much enlarged.) 



the galls will be so small as 

 be capable of crowding. In 

 a tiny footless maggot-like w 

 through the skin, on the sap 

 which it Ues. With the birth 



(Fig. 655) are all very small, the largest 

 species not being more than i 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 



to draw but little on the plant-stores and 



two or three weeks the egg gives birth to 



hite larva which feeds, undoubtedly largely 



abundantly flowing to the growing tissue in 



of the larva begins the development of the 



Fig. 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 (.\ftcr Lacaze- 

 Duthiers; greatly magnified.) 



gall, which is an abnormal or hj'pertrophied 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 



