INSECTA 



117 



slugs. The horn-tails (Siricidce) are related to the saw- 

 flies. The females have a long hard ovipositor at the end 

 of the abdomen with which they drill holes in trees. The 

 larvae burrow in the heart wood and grow into white grubs. 

 The gall-flies (Cynipidce) lay eggs in living buds, leaves, 

 or stems, and their larvae develop inside galls which develop 

 on the plants attacked. Though such abnormal growths 

 are found on many plants they are most common on the 



FIG. 57. Hymenoptera. Chalcid-fly and cocoons on caterpillar; bees and 

 wasps; ichneumon-flies; horn-tail larva. 



oak, rose, and hickory. All the gall-flies are of small size, 

 the largest being only a third of an inch long. The galls 

 produced by different species are quite characteristic. 

 They present a great variety of forms rosettes, stars, 

 spheres, and other shapes. The growth of a gall is due to 

 the irritation from the developing larva within. Some 

 gall-flies do not form galls of their own, but lay their eggs 

 in the growths produced by other species. 



