466 Saw-flies, Gall-flies, Ichneumons, 



no males have yet been discovered. It is indeed a general rule in the family 

 that the females greatly outnumber the males. 



Probably our most familiar saw-fly, at least in its larval stage, is the 

 rose-slug, Monostegia rosce, a soft-bodied, greenish-yellow, nocturnal larva 

 that skeletonizes rose-leaves and often occurs in such' numbers as practically 

 to defoliate the bushes. The adult fly is black with sooty wings and whitish 

 fore and middle legs. There are two generations a year. Two currant- 

 slugs are common: one the imported currant-worm, Nematus ventncosus 

 (Fig. 652), green with many small black spots (in its last stage only the head 

 is black-spotted); the other the native currant-worm, Pristophora grossu- 

 larice, all pale green except the blackish head, which becomes partly green 

 just before pupation. Both of these slugs make slight cocoons of silk and 

 leaves in which to pupate, the first-named one in or on the ground, the second 

 one attached to the twigs or leaves of the currant-bush. 



The pear-tree slug, Eriocampa cerasi, is half an inch long when full-grown, 

 with the body expanded in front so as to be almost tadpole-shaped; it is 

 greenish with a gummy slime over it. It feeds in May and June on the 

 upper surfaces of the leaves, and when full-grown crawls down to the ground 

 and makes a little cell just below the surface in which to pupate. The 

 winged saw-fly is glossy black, about inch long. The eggs are laid in 

 slits cut on the under side of the leaves. The larch is often seriously attacked 

 by the larva of the saw-fly Nematus erichsonii; it is a glaucous green slug 

 with jet-black head and two double rows of tiny black points around the 

 abdomen; it is -f inch long and has seven pairs of prop-legs. The adult, 

 J- inch long, is thick-bodied, blackish with a broad bright resin-red band on 

 the abdomen. The eggs are laid in the young shoots in June or July, the 

 larvse feeding until late in July or early in August. In California one of 

 the most abundant saw-flies is a species of Lyda, which lays its eggs in the 

 summer on the new growth of needles on pines. The larvae hatch out 

 in fifteen days and feed on the needles for four months; then they trans- 

 form to another larval stage, migrate to the tops of the trees, and just 

 before winter spin a silken cocoon in which they pupate. The adult flies 

 issue in the spring. 



A much smaller family than that of the saw-flies is the nearly related 

 one of the horntails, the Siricidae. About fifty species are known in this 

 country. The females are provided with a boring ovipositor, which appears 

 as a conspicuous, strong, long "horn," projecting from the tip of the abdo- 

 men; Comstock describes this ovipositor as composed of five long slender 

 pieces; the two outside pieces are grouped on the inner surface, and when 

 joined make a sheath containing the other three pieces, two of which are 

 furnished at the tip with fine transverse ridges like the teeth of a file. With 

 this boring ovipositor the female can drill holes into the solid wood of a tree 



