OF SELBOENE. 
185 
skeltered districts, over some lake, or under some hanging 
wood, or in some hollow vale, especially in windy weather. 
They breed the latest of all the swallow kind: in 1772 
they had nestlings on to October the 21st, and are never 
without unfledged young as late as Michaelmas. 
As the summer declines, the congregating flocks increase 
in numbers daily, by the constant accession of the second 
broods ; till at last they swarm in myriads upon myriads 
round the villages on the Thames, darkening the face of the 
sky as they frequent the aits of that river where they 
roost. They retire (the bulk of them I mean) in vast flocks 
together, about the beginning of October : but have ap- 
peared of late years in a considerable flight in this neigh- 
bourhood, for one day or two, as late as JSTovember the 3rd 
and 6th, after they were supposed to have been gone for 
more than a fortnight. They therefore withdraw with us 
the latest of any species. Unless these birds are very 
short-lived indeed, or unless they do not return to the 
district where they are bred, they must undergo vast 
devastations somehow, and somewhere ; for the birds that 
return yearly bear no manner of proportion to the birds that 
retire. 
House martins are distinguished from their congeners 
by having their legs covered with soft downy feathers down 
to their toes. They are no songsters; but twitter in a pretty 
inward soft manner in their nests. During the time of 
breeding, they are often greatly molested with fleas. ^ 
^ Allusion has been already made to the parasites of swallows in the 
previous letter, p. 180, and some further remarks on the subject will be 
found later on in Letters XX. and XXI. Should the reader be curious 
to learn something more of these singular insects, reference may be made 
with advantage to Denny's " Monographia Anoplurorum Britannia^," an 
essay on the British species of parasitic insects. — Ed. 
/ 
