22 PRIZE essay: 



24. Not less than two hundred kinds of caterpillars are sup- 

 posed to feed upon the oak ; and upwards of 50 different species 

 of insects are known to live upon the nettle, which is so repug- 

 nant to quadrupeds that few will touch it, yet such is the rapid 

 increase of this vegetahle, that if it were not for its insect de- 

 predators it would soon annihilate all plants in its neighbour- 

 hood. The naturalist, Wilke, tells us that every plant has its 

 proper insect allotted to it, to curb its luxuriance and to prevent 

 it from multiplying to the exclusion of others. The peculiarity 

 of the agency of insects consists of their power of suddenly 

 multiplying their numbers to a degreee which could only be 

 accomplished in a considerable lapse of time in any of the larger 

 animals, and then as instantaneously relapsing without the inter- 

 vention of any violent disturbing cause into their former insig- 

 nificance. (') Many instances of this sudden increase and cor- 

 responding disappearance a few days or weeks after, will be 

 noticed in the folloAving pages. 



25. The wind seems to play a very important part in the dis- 

 tribution of insects over wide areas and in particular directions. 

 A wind from the coast of Africa drove such myriads of flies upon 

 the fresh paint of H. M. S. Adventure, then 100 miles from 

 land, that not the smallest point was left unoccupied or uncov- 

 ered. The Hessian fly, and particularly the wheat midge, both 

 select low and sheltered places for their depredations. Elevated 

 and exposed fields are not unfrequently untouched in the midst 

 of the greatest devastation 



26. The connection of insects with rocks is a subject which 

 has been investigated to a very slight degree, and offers a fertile 

 and instructive field for the enquiring agricultural entomologist. 

 Mr. Wailes always found the larvse of enicoceri on rough shiny 



(1) Lyell— Principle of Geology. 



