It is probable that these spiders have in times past learned by experience that they cannot do better than take such materials as come to hand, as these will ordinarily serve for the concealment of their door. However, these trap-door spiders do seem to exercise some discrimination in the choice of materials; for I have observed several instances in which, when the door of a cork nest has been removed, if the door was originally covered with moss, moss will again be used in its reconstruction, even though the mouth of the tube be then surrounded by bare earth. Thus, for example, in one case where I had cut out a little clod of mossy earth, about two inches thick and three square on the surface, containing the top of the tube and the moss-covered cork door of _N. cæmentaria_, I found, on revisiting the place six days later, that a new door had been made, and that the spider had mounted up to fetch moss from the undisturbed bank above, planting it in the earth which formed the crown of the door.[80] Here the moss actually called the eye to the trap, which lay in the little plain of brown earth made by my digging. [Footnote 80: Mrs. Boyle first called my attention to this curious fact, of which I have since seen many examples. I have purposely removed several cork doors from mossy banks in order to observe this point.] I have seen the same thing happen when the door of _N. Eleanora_ has been removed and replaced, moss being again used in the work of reconstruction. Trap-door spiders in warm weather very quickly replace their trap-doors; and if you pass by a wall where several nests have been robbed of their doors only a week before, they will usually be found quite perfect again. It has been stated[81] that, if the door of a cork nest be fastened down with a pin, a second door will be found next day by the side of the former one. No doubt spiders not unfrequently find their doors blocked up by a fall of earth, and are thus obliged either to make a new opening or to prolong the old tube. [Footnote 81: M. Dorthès on the Structure and Œconomy of some Curious Species of Aranea, in Trans. Linn. Soc. (London), II. 88-90.] I once fastened open the surface doors of three of the double-door nests by passing a thread through the silk of the door and tying it back to some twigs above. The doors were thus turned backwards, and the aperture of the tubes, which lay in a vertical terrace wall, exposed to view.