Page:White - The Natural History and Antiquities of Selborne.djvu/197

 that these beginnings were intentionally made in order to be in the greater forwardness for next spring, is allowing perhaps too much foresight and rerum prudentia to a simple bird. May not the cause of these latebrae being left unfinished arise from their meeting in those places with strata too harsh, hard, and solid, for their purpose, which 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 threatening to overwhelm them and their labours ?

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 untenable. This species of swallow moreover is strangely annoyed with fleas: and we have seen fleas, bed-fleas (pulex irritans), swarming at the mouths of these holes, like bees upon 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 the 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 somewhat 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 libellulae (