210 NATURAL HISTORY 
claws, should ever be able to bore the stubborn 
sandbank without entirely disabling herself; yet 
with these feeble instruments have I seen a pair of 
them make great despatch, and could remark how 
much they had scooped that day by the fresh sand 
which ran down the bank, and was of a different 
colour from that which lay loose and bleached in 
the sun. 
In what space of time these little artists are able 
to mine and finish these cavities I have never been 
able to discover, for reasons ‘given above; but it 
would be a matter worthy of observation, where it 
falls in the way of any naturalist, to make his re- 
marks. This I have often taken notice of, that 
several holes of different depths are left unfinished 
at the end of summer. ‘To imagine that these be- 
ginnings were intentionally made, in order to be in 
the greater forwardness for next spring, is allow- 
ing, perhaps, too much foresight and rerum pruden- 
tia to a simple bird. May not the cause of these 
latebre being left unfinished arise from their meet- 
ing 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 founder, 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 untenantable. 
This species of swallow, moreover, is strangely 
annoyed with fleas; and we have seen fleas, bed- 
