OYSTER-SHELL BARK-LOUSE. 25 



The parts of the mouth are undeveloped, so that it takes no food, 

 his sole office being the propagation of the species. 



The female, on the other hand, with which alone we are ac- 

 quainted, and which has been, upon the whole, probably the worst 

 enemy that the orchardist, in the Northern States, has had to 

 contend with, is a wingless, footless, eyeless, grub-like creature, 

 which never moves from the spot where she first fixes herself, 

 and effectually excludes herself from the light of day, by inclosing 

 herself in au impervious cell, as it were, in a living sepulchre. 

 And yet, though destitute both of the organs of vision and loco- 

 motion, these insects have passed from one continent to another, 

 spread over vast States and Territories, crippled or destroyed 

 thousands of orchards, and impoverished their owners, in spite of 

 all the efforts and appliances which human ingenuity could de- 

 vise. And the difficulty is increased when we consider that, with 

 the exception of the first three or four days of their lives, they 

 are immovably fixed to the bark of the tree. Can the mystery 

 be solved ? 



In the first place, it is evident that this insect, if indeed it be 

 identical with the European species, must have been brought 

 across the ocean, attached to the bark of nursery trees. But it is 

 far from being so easy to explain how it has been carried from 

 one tree, and from one orchard to another, often at great distances 

 apart. 



Three theories have been suggested upon this subject ; first, 

 that the insects transport themselves during the short active pe- 

 riod of their lives, by crawling from one tree to another. It 

 seems to me that a very little observation must convince us that 

 this theory is wholly untenable. If we compare the roughness of 

 a piece of plowed ground, or the inequalities of sod land, with its 

 growing grass and itc complicated matting of last year's growth, 

 with the microscopic minuteness of these insects, during the short 

 active period of their existence, it will be obvious that they never 

 could migrate more than two or three feet, at most, from the tree 

 on which they grew, by any locomotive powers of their own. 



Another theory is that they are carried from one place to an- 

 other by adhering to the feet of birds, and possibly also to the feet 

 and legs of larger insects. This was Mr. Walsh's theory, and it 

 seems to be the only way in which we can account for their being 

 carried to any considerable distance, such for instance as a mile 



A— 4: 



