OF SELBORNE. 293 
of the black shining cases of the hippobosca hirun- 
dinis. 
The following remarks on this unusual incident 
are obvious. ‘The first is, that though it may be 
disagreeable to swifts to remain beyond the begin- 
ning of August, yet that they can subsist longer is 
undeniable. The second is, that this uncommon 
event, as it was owing to the loss of the first brood, 
so it corroborates my former remark, that swifts 
have but one regularly; since, was the contrary 
the case, the occurrence above could neither be 
new nor rare. 
One swift was seen at Lyndon, in the county of 
Rutland, in 1782, so late as the 3d of September. 
LETTER XLIX. 
s 
As I have sometimes known you make inquiries 
about several kinds of insects, I shall here send 
you an account of one sort which I little expected 
to have found in this kingdom. I had often ob. 
served that one particular part of a vine, growing 
on the walls of my house, was covered in the au- 
tumn with a black dust-like appearance, on which 
the flies fed eagerly, and that the shoots and leaves 
thus affected did not thrive, nor did the fruit ripen. 
To this substance I applied my glasses, but could 
not discover that it had anything to do with animal 
life, as I at first expected ; but, on a closer exam- 
ination behind the larger boughs, we were sur- 
prised to find that they were coated over with 
husky shells, from whose sides proceeded a cotton- 
BB2 
