468 Saw-flies, Gall-flies, Ichneumons, 
Cynipid gall-flies. These 
flies (Fig. 655) are all very small, the largest 
species not being more than -J- 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 
Fig. 655.—A gall-fly, species unde¬ 
termined. (Much enlarged.) 
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 (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 
