In forming the burrow the spider carries out the clay bit by bit, and when it reaches a point below the surface it begins to line the sides with a silken tapestry. The door is an upper extension of this lining. It is round, about the size of a silver quarter, or a little larger, and is formed of silk so woven and interwoven that it becomes a pad of seeming satin, which by continued manipulation is made to fit with marvelous perfection. The spring or hinge is so adjusted that the door always closes, and with a snap. The exterior of the door is covered with clay, and is made to simulate the surroundings so exactly that only the sharpest eye, and one skilled in the work, can distinguish it. In some of the European spiders of this kind the door is carefully covered with moss and plants. The work of building is done at night. The spiders feed at night, and in returning to the burrow they can lift the lid instantly, dart in, and turn about to seize the cushion or pad of the door with their fangs, and hold it so tightly by bracing back that some little strength is needed to force it. I have often lifted the door with the blade of my knife and seen the spider rush up and seize it. In all the doors little round holes can be seen where the mandibles or fangs hold. The spider can be caught by pouring water into the burrow and forcing it out. In the island of Timos there is a trapdoor spider which does not hunt, but combines the methods of other spiders. It comes out at night, fastens back its door by a thread, then builds a web near by and waits for its victims to become entangled. [Illustration: FIG. 179.--A chimney-building spider.] The largest spiders are called tarantulas, though the term is applied to some forms not so large. They are hideous creatures, and are very common in southern California. They are five or six inches across the legs, and the body in some forms is as large as a small mouse, and is covered with reddish hair. They form deep burrows, but not trapdoors, the entrance being open or covered by a web. They are supposed to be very poisonous. Mygale Hentzii is the name of the common American species found in the southwest (Fig. 177). They hunt at night for grasshoppers, crickets, and other small game, and can often be seen lumbering along over the roads at sunrise, returning from a hunt. Sometimes these huge spiders migrate in a body, such a movement having been observed in southern California.