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THE NATURAL HISTORY OF SELBORNE. ~ 155 
they relinquish, and go to a fresh spot that works more freely ? 
Or may they not in other places fall in with a soil as much too 
loose and mouldering, liable to flounder, and sabes > to 
overwhelm them and their labors ? 
One thing is remarkable —that, after some years, the old 
holes are forsaken and new ones bored ; perhaps because the 
old habitations grow foul and fetid from long use, or because 
they may so abound with fleas as to become untenantable. 
This species of swallow moreover is strangely annoyed with 
fleas; and we have seen fleas, bed-fleas, swarming at the 
mouths of these holes, like bees on the stools of their hives. 
The following circumstance should by no means be omitted, 
that these birds do not make use of their caverns by way of 
hybernacula, as might be expected; since banks so perforated 
have been dug out with care in the winter, when nothing was 
found but empty nests. 
The sand-martin arrives much about the same time with the 
swallow, and lays, as she does, from four to six white eggs. 
But as this species is carrying on the business of nidification, 
incubation, and the support of its young in the dark, it would 
not be so,easy to ascertain the time of breeding, were it not 
for the coming forth of the broods, which appear much about 
the time, or rather somewhat earlier than those of the swallow. 
The nestlings are supported in common like those of their con- 
geners, with gnats and other small insects; and sometimes they 
are fed with dragon-flies almost as long as themselves. In the 
last week in June we have seen a row of these sitting on a rail 
near a great pool as perchers, and so young and helpless as 
_ easily to be taken by hand; but whether the dams ever feed 
them on the wing, as swallows and house-martins do, we have 
never yet been able to determine; nor do we know whether 
they pursue and attack birds of prey. 
When they happen to breed near hedges and enclosures, 
they are dispossessed of their breeding-holes by the house- 
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