"Many species of birds have their peculiar lice; but the hirundines alone seem to be annoyed with dipterous insects, which infest every species, and are so large, in proportion to themselves, that they must be extremely irksome and injurious to them. These are the hippoboscæ hinindinis, with narrow subulated wings, abounding in every nest; and are hatched by the warmth of the bird's own body during incubation, and crawl about under its feathers.
"A species of them is familiar to horsemen in the south of England under the name of forest-fly; and to some of side-fly, from its running sideways like a crab. It creeps under the tails, and about the groins, of horses, which, at their first coming out of the north, are rendered half frantic by the tickling sensation; while our own breed little regards them.
"The curious Reaumur discovered the large eggs, or rather pupæ, of these flies as big as the flies themselves, which he hatched in his own bosom. Any person that will take the trouble to examine the old nests of either species of swallows may find in them the black shining cases or skins of the pupa of these insects; but for other particulars, too long for this place, we refer the reader to 'L'Histoire d'Insectes' of that admirable entomologist. Tom. iv., pi. ii."
NOTE TO LETTER XV.
The white owl does hoot, although it is not its most frequent cry.
LETTER XVI.
Dear Sir,—In obedience to your injunctions I sit down to give you some account of the house-martin, or martlet; and if my monography of this little domestic and familiar bird should happen to meet with your approbation, I may probably soon extend my inquiries to the rest of the British hirundines—the swallow, the swift, and the bank-martin.
