NATURAL HISTORY OF SELBORNE. 171 



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 (Pulex irritans), 

 swarming at the mouth 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 cryptogame, 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 some- 

 what earlier than those of the swallow. The nestlings are 

 supported in common like those of their congeners, with 

 gnats and other small insects ; and sometimes they are fed 

 with libellulce (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- 

 sparrow, which is on the same account a fell adversary to 

 house-martins. 



