52 NATURE SKETCHES IN TEMPERATE AMERICA 



formed \^ the twigs and petioles of the flower buds. The 

 young, after hatching from these eggs, settle down on the 

 side toward the twig near the base. In one of the grooves of 

 the buds, the young individual called tJie stem mother (see 

 plate) inserts her beak, and feeding on; the juices, together 

 with some subtle, irritating substance which she injects, causes 

 the remarkable transformation of the embryo bud into the 

 spiny gall. The formation of the young gall is quite rapid, 

 the bud on the side toward the insect lengthening and growing 

 over the gall-maker. At first it is a rosy color, but after a 

 time, when it becomes about half-grown, it loses the red tint 

 and becomes green. By the end of June or the beginning of 

 July it is mature. Within the chambered house, the stem 

 mother has become very prohfic, giving birth to as many as 

 two hundred of her own progeny. Early in July, or about a 

 month and a half after the hatching of this stem mother, the 

 earliest migrants, her descendants, are fully developed. They 

 then commence leaving the gall and continue to issue forth 

 until late in the fall, migrating to the leaves of the birches 

 where they deposit their larvae. The latter, after feeding on 

 the birch leaves, settle down close to the bud, getting ready for 

 their transformation and for hibernation. 



These larvae represent the third, or Coccidiform, generation 

 and their growth is very slow, many of them perishing here 

 before spring, so that few adult feroales survive. These 

 Coccidiform adults that come forth deposit their larvae on the 

 tender leaflets just budding out. By their sucking process, 

 irritation is set up at the edges of the young leaves, making 

 certain changes that cause them to turn :down and also cause 

 bulging of the upper surface. This gives rise to corrugation, 

 or pseudo-galls, of reddish or crimson color. It must be remem- 

 bered that this is quite a different gall from the spiny gall on 

 the witch-hazel, yet produced by the same insect species. 



Between the folds of the gall these insects live and grow 

 rapidly, reaching full development by the end of April or early 

 May. The fourth generation is quite unlike the Coccidiform 

 generation. It is during the fifth generation that the winged 

 return migrant is produced, which is much smaller than those 

 leaving the witch-hazel, and it returns to the witch-hazel 



