* * * * *
[It will be proper to premise here that the sixteenth, eighteenth,
twentieth, and twenty-first letters have been published already in the
"Philosophical Transactions;" but as nicer observation has furnished
several corrections and additions, it is hoped that the republication of
them will not give offence; especially as these sheets would be very
imperfect without them, and as they will be new to many readers who had
no opportunity of seeing them when they made their first appearance.]
"The hirundines are a most inoffensive, harmless, entertaining, social,
and useful tribe of birds; they touch no fruit in our gardens; delight,
all except one species, in attaching themselves to our houses; amuse us
with their migrations, songs, and marvellous agility; and clear our
outlets from the annoyances of gnats and other troublesome insects. Some
districts in the south seas, near Guiaquil, are desolated, it seems, by
the infinite swarms of venomous mosquitoes, which fill the air, and
render those coasts insupportable. It would be worth inquiring whether
any species of hirundines is found in those regions. Whoever
contemplates the myriads of insects that sport in the sunbeams of a
summer evening in this country, will soon be convinced to what a degree
our atmosphere would be choked with them was it not for the friendly
interposition of the swallow tribe.
"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 _hippoboscoe
hirundinis_, 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 _pupoe_, 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 _pupoe_ 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., pl. ii."