MOUNTAIN TREES 



the tender growing tissues of the leaf or 

 twig and there lays her eggs. In two or 

 three weeks tiny footless larvae are born 

 and begin to feed upon the sap of the 

 vascular plant tissue in which they lie 

 embedded. Then with the salivary se- 

 cretions and physical irritation produced 

 by the larvae as the exciting cause, the 

 gall begins to grow, and never ceases its 

 abnormal development until the larvae 

 reach their full growth. Upon maturing 

 of the larvae, the gall begins to dry up 

 and harden, thus forming a snug 

 house for the insects during their period 

 of pupation. Later upon development 

 into full grown flies, the tiny insects 

 gnaw their way out of the dead galls to 

 prick in new leaves and lay eggs for an- 

 other life cycle. 



These gall flies are tiny two-winged 

 insects, the largest being not more than 

 one-third of an inch long. Curiously, 

 the individuals of some species are all 

 females. An additional interesting fea- 

 ture is the fact that often in the same 



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