20 Our Field and Forest Trees 



branch does, for some mother gall-flies make their 

 nurseries in the wood. 



After a branch has been pierced, and the egg 

 put in, the wood around it becomes diseased, 

 changes color, and grows into a queer lump or 

 knob. In the heart of every such lump there is a 

 grub, or an empty chamber where a grub used to 

 live before it took to itself wings and flew away. 

 Gall-flies of many sorts and sizes attack the oak. 

 The strongest and sturdiest of the trees is the 

 one that suffers the most from these stinging 

 enemies. They pierce the buds, the baby acorns, 

 the leaves, the bark, and the wood; and on the 

 much-enduring oak we see galls of many sorts, 

 shapes, and sizes. Some cradle one grub, living 

 and feasting in solitude, some are providing food 

 and shelter for a large family. 



On the willows, especially on the low-growing 

 pussy willow of the swamps, one sees many a 

 reminder that even the most innocent life may have 

 its enemies. Some of the twigs are tipped with 

 black lumps, covered with scales and looking so 

 much like pine cones that they are called " pine- 

 cone willow galls." These are made by a little 

 black fly, which visits the bushes in the spring, 

 when the leaf buds are beginning to unfold. She 

 chooses the topmost bud of a branch, pierces it, 

 and puts a single tiny egg into the hole she has 

 made (Fig. 8). 



Soon the spring warmth hatches, from this egg. 



