Occasionally we found one about half the usual size, indicating a young spider, but no other sizes. My guide said they only emerge from their tunnel at night, and proved it by an ingenious mechanical device made of straws attached to the door. When the door was opened, the straws lifted up, but did not fall down when it was closed. Whenever he found the straw still up in the morning he knew the door had been opened in the night.
As they are nocturnal in habits, they doubtless prey upon other insects, such as sow-bugs and crickets, which the night brings forth. Two bright specks upon the top of the head appear to be eyes, but they are so small they probably only serve to enable them to tell night from day. I think these spiders are mainly guided by a marvelously acute tactile sense. They probably feel the slightest vibration in the earth or air, unless they have a sixth sense of which we know nothing.
All their work, the building and repairing of their nests, as well as all their hunting, is done by night. This habit, in connection with their extreme shyness, makes the task of getting at their life-histories a difficult one. The inside of the burrow seems coated with a finer and harder substance than the soil in which they are dug. It is made on the spot, the spider mixing some secretion of her own with the clay, and working it up into a finer product.
The trap-door sooner or later wears out at the hinge, and is then discarded and a new door manufactured. We saw many nests with the old door lying near the entrance. The door is made of several layers of silk and clay, and is a substantial affair.
The spider families all have the gift of genius. Of what ingenious devices and arts are they masters! How wide their range! They spin, they delve, they jump, they fly. They are the original spinners. They have probably been on their job since carboniferous times, many millions of years before man took up the art. And they can spin a thread so fine that science makes the astonishing statement that it would take four millions of them to make a thread the caliber of one of the hairs of our head—a degree of delicacy to which man can never hope to attain.
Trap-doors usually mean surprises and stratagems, secrets and betrayals, and this species of the arachnids is proficient in all these things.
The adobe soil on the Pacific coast is as well fitted to the purposes of this spider as if it had been made for her special use. But, as in all such cases, the soil was not made for her, but she is adapted to it. It is radically unlike any soil on the Atlantic coast—the soil for cañons and the rectangular watercourses, and for the trap-door spider. It is a tough, fine-grained homogeneous soil, and when dry does not crumble or disintegrate; the cohesion of particles is such that sun-dried brick are easily made from it.
This spider is found in New Mexico, Arizona, California, and Jamaica. It belongs to the family of Mygalidae. It resembles in appearance the tarantula of Europe, described by Fabre, and has many of the same habits; but its habitation is a much more ingenious and artistic piece of workmanship than that of its European relative. The tarantula has no door to her burrow, but instead she builds about the entrance a kind of breastwork an inch high and nearly two inches in diameter, and from this fortress sallies out upon her prey. She sinks a deeper shaft than does our spider, but excavates it in the same way with similar tools, her fangs, and lines it with silk from her own body.
Our spider is an artist, evidently the master builder and architect of her kind. Considering her soft and pussy-like appearance—no visible drills for such rough work—one wonders how she excavates a burrow six inches or more deep in this hard adobe soil of the Pacific coast, and how she removes the dirt after she has loosened it. But she has been surprised at her work; her tools are her two fangs, the same weapons with which she seizes and dispatches her prey, and the rake or the cheliceræ. To use these delicate instruments in such coarse work, says Fabre, seems as "illogical as it would to dig a pit with a surgeon's scalpel." And she carries the soil out in her mandibles, a minute pellet at a time, and drops it here and there at some distance from her nest. Her dooryard is never littered with it. It takes her one hour to dig a hole the size of half an English walnut, and to remove the earth.
One afternoon I cut off the doors from two nests and left them turned over, a few inches away. The next morning I found that the occupants of the nests, under cover of the darkness, had each started the construction of a new door, and had it about half finished. It seemed as if the soil on the hinge side had begun to grow, and had put out a semicircular bit of its surface toward the opposite side of the orifice, each new door copying exactly the color of the ground that surrounded it, one gray from dead vegetable matter, the other a light brick-red. I read somewhere of an experimenter who found a nest on a mossy bit of ground protectively colored in this way. He removed the lid and made the soil bare about. The spider made a new lid and covered it with moss like the old one, and her art had the opposite effect to what it had in the first case. This is typical of the working of the insect mind. It seems to know everything, and yet to know nothing, as we use the term "know."