Insect Study 



361 



Oak apple, showing the larva of the gall insect. 



Comstock's Manual. 



We may take the history of the common oak apple, as an example. 

 A little, four-winged, fly-like creature lays its eggs, early in the season, 

 on the leaf of the scarlet oak. As soon as the larva hatches, it begins to 



eat into the substance of 

 one of the leaf veins. As it 

 eats, it discharges through 

 its mouth into the tissues 

 of the leaf, a substance 

 which is secreted from 

 glands within its body. 

 Immediately the building 

 of the house commences; 

 out around the little crea- 

 ture groAv radiating vegeta- 

 ble fibers, showing by their 

 position plainly that the 

 grub is the center of all of 

 this new growth; mean- 

 while, a smooth, thin cover- 

 ing completely encloses the 

 globular house; larger and 

 larger grows the house 

 until we are accustomed 

 to call it an oak apple, so 

 large is it. The little chap 

 inside is surely content and 

 happy, for it is protected from the sight of all of its enemies, and it 

 finds the walls of its house the best of food. It is comparable to a boy 

 living in the middle of a giant sponge cake, and who when hungry would 

 naturally eat out a larger cave in the heart of the cake. After the inmate 

 of the oak apple completes its growth, it changes to a pupa and finally 

 comes out into the world a tiny four-winged fly, scarcely a c|uarter of an 

 inch in length. 



The story of the willow cone-gall is quite different. A little gnat lays 

 her eggs on the tip of the bud of a twig; as soon as the grub hatches and 

 begins to eat, the growth of the twig is arrested, the leaves are stunted 

 until they are mere scales and are obliged to overlap in rows around the 

 little inmate, thus making for it a cone-shaped house which is very 

 thoroughly shingled. The inhabitant of this gall is a hospitable little 

 fellow, and his house shelters and feeds many other insect guests. He 

 does not pay any attention to them, being a recluse in his own cell, but 

 he civilly allows them to take care of themselves in his domain, and 

 feed iipon the walls of his house. He stays in his snug home all winter 

 and comes out in the spring a tiny, two-winged fly. 



There are two galls common on the stems of goldenrod. The more 

 numerous is spherical in form and is made by a fat and prosperous 

 looking little grub which later develops into a fly. But although it 

 is a fly that makes the globular gall in the stem of goldenrod, the 

 spindle-shaped gall often seen on the same stem has quite another 

 story. A little brown and gray mottled moth, about three-fourths of an 

 inch long, lays her egg on the stem of the young goldenrod. The cater- 

 pillar, when it hatches, lives inside the stem, which accommodatingly 



