35 
[ 295 ] 
The following extract from this article presents some interest¬ 
ing observations not otherwise stated in the body of this report. 
The causes which have been instrumental in producing the de¬ 
struction of the Oyster-shell Bark-louse, and which are still opera¬ 
ting to its completion, are matters of much interest. The agencies 
to which it has been usually attributed are the four following : In¬ 
sectivorous birds j predaceous insects, especially the Coccinellce , 
or Lady-bugs, and their larvse } the larvse ot the parasitic Chalcis- 
fiies, and the Mites, or Acari. 
It has been generally supposed that the smaller insectivorous 
birds, such as the wrens and warblers, devour many of the eggs of 
the Bark-louse, but these eggs are so minute and so completely 
concealed under the bark-like scales, that even the sharp eyes of 
a bird could scarcely detect them, unless it were endowed with a 
special instinct for the purpose, and I know of no record of any 
actual observations which confirm this supposition. I am there¬ 
fore inclined to the opinion that birds have done little or nothing 
in the way of exterminating the Bark-louse. 
The Coccinellce devour a very small proportion of these insects, 
whilst they are in their incipient and active state ; but this lasts 
only three or four days, and therefore but very few of them can be 
thus destroyed. These predaceous insects, and especially their 
larvge, also destroy a few of the bark-hce, in their subsequent sta¬ 
ges, by gnawing ragged holes through the scales, and thus getting 
access to the insect beneath. Mr. Walsh conjectured that these 
rough holes were made by Acari , but I have repeatedly seen the 
larva of the Two-spotted Coccinella in the act of gnawing just such 
holes in the scales of the Bark-louse of the pine tree, and devour¬ 
ing its contents, and it is therefore probable that they are the au¬ 
thors of the similar holes on the apple tree. But the small num¬ 
ber of scales eaten into shows that but few bark-lice are destroyed 
in this way. 
The destructive work of the Acari is supposed to be indicated by 
the brownish, discolored remnants of the eggs from which the 
contents seem to have been extracted, easily distinguished from 
the pure white shells from which the insects have been hatched. 
Both Mr. Walsh and Dr. Shimer, who were the first to notice 
these mites, attribute much efficacy to their depredations, but that 
they are the sole authors of this work is rendered somewhat doubt- 
