CHAPTER III. 

 THE NUMERICAL ASPECT OF OAK GALLS. 



The great abundance of many species of oak galls is 

 often commented npon by field naturalists, but the 

 phenomenon is seldom referred to in publications. It 

 is, however, a feature which annually manifests itself 

 in a most pronounced manner. 



In districts where hedge-banks are neglected, and 

 woods are not cut dow^n more than once in twelve or 

 fourteen years, the gall-wasps have every facility to 

 multiply and spread unchecked — an advantage of which 

 they fully avail themselves. 



The diminutive size of most species doubtless affords 

 them considerable immunity from the voracity of car- 

 nivorous insects, nor do they often become the food of 

 spiders. If the snare of almost any sylvan spider be 

 examined, it will be found that captive insects are 

 very few whose wing expanse is less than I'o or 2 mm. 

 As the strands of most snares are from 5 mm. to 10 mm. 

 apart, and some much wider, it may be assumed that 

 numbers of the smaller Cynipidas pass through the 

 meshes without detention, while larger insects are en- 

 tangled in the sticky threads. 



Doubtless they are enabled to escape the notice of 

 many enemies on account of their lethargic hal^its, and 

 a tendency to simulate death. 



The main factor, however, in the abundance of galls, 

 is the prodigious number of ova these tiny insects are 

 capable of producing, and also the leisurely and 

 effective manner in which they oviposit. An instance 

 observed and recorded by Dr. Adler is perhaps the 

 most enlightening concerning this. An imago of 

 Biorliiza aptera "was put upon a little oak, and soon 

 began to prick a bud ; when it had finished the first 



