CHAPTER III. 
THE NUMERICAL ASPECT OF OAK GALLS. 
THE great abundance of many species of oak galls is 
often commented upon 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 down 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. Ifthe snare of almost any sylvan spider be 
examined, it will be found that captive insects are 
very few whose wing expanse is less than 1°5 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 Cynipide 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 habits, 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 
Biorhiza aptera “was put upon a little oak, and soon 
began to prick a bud; when it had finished the first 
