HYMENOPTERA 227 



leaves of pines. The larvae live socially, feeding on the leaves 

 and young shoots, and resting on the leaves, with the head 

 bent to one side. In July they form relatively small cocoons 

 (about 6 mm. long) on the leaves or twigs, from which the 

 flies emerge a fortnight later. A second brood is then pro- 

 duced, which, when full-fed, enters the earth, or hides in fallen 

 leaves, moss, etc., about the roots, and yields the flies of 

 spring. But larvse of the early brood occasionally pupate in 

 the earth, and the second brood may remain long unchanged 

 underground. Several other species of Lophyrus are found 

 on pines. Trees which are well exposed to light and air are 

 more often attacked than others. 



The turnip saw-fly {Athalia spinaruni) is best known in the 

 larval stage. The eggs are laid in May or June in slits on 

 the margin of turnip-leaves. The larvae resemble small black 

 caterpillars, and are hence called "blacks," "niggers," etc. 

 They feed in great numbers on the leaves of the turnip and 

 other Cruciferse, gnawing the edges, and at length leaving only 

 the larger veins. They have eleven pairs of feet, and are 

 at first pale, then green, and finaUy dark, except beneath and 

 along the side, where there is a pale stripe. They are fond 

 of warmth, and feed most busily in hot weather. Young larvae, 

 when disturbed, let themselves down by a thread ; older ones 

 drop to the ground. They become full-fed in about five weeks, 

 and are then 17 mm. long. They enter the earth, make a 

 silken cocoon, and pupate. A second brood of flies appears 

 in August. The autumn larvae enter the earth, and remain 

 unchanged till spring, when they pupate, turning to flies in 

 early summer. The fly is 7 mm. long, of orange-yellow colour, 

 with the head, part of the thorax, and the extremities of the 

 legs, black. The wings are yellow at the root and black along 

 the fore edge of the fore wing, a coloration very common in 

 saw-flies. 



The corn-saw-fly (Cephus pygmaus) differs in some particulars 

 from other saw-flies, though it has the characteristic saws ; it 

 probably represents a primitive section of the family. The fly 

 has an elongate thorax and a pointed abdomen ; it is yellow- 

 coloured, and 7 mm. long. The eggs are laid on young stems 

 of corn, and the larvse which issue from them are soft, yellow, 

 and apparently footless grubs ; on close examination, however, 

 minute thoracic legs can be discovered, A larva eats its way 



