National Geographic : 1933 Aug
CALIFORNIA TRAPDOOR SPIDER PERFORMS ENGINEERING MARVELS BY LEE PASSMORE With Illustrations from Photographs by the Author and F. E. Beck R ETURNING one May evening from a ramble over the southern Califor nia foothills, I came across a young man busily digging in a small mossy knoll. He was so engrossed in his work that he did not become aware of my presence until my shadow fell upon the object which was attracting his attention. With apologies for my intrusion, I asked what he was digging. He turned with a pleasant smile and replied, "Trapdoor spiders." Then, reaching down into the hole, he handed me a strange tubular object, warn ing me that it was exceedingly fragile-an exceptionally fine specimen of a cork-type spider's nest. The burrow, or nest, about ten inches long by one and a half inches wide, was built in adobe soil. Fitting neatly in its upper end was a door, hinged with tough web. The under surface of this cover and the walls of the tube were lined with smooth, silky web of lustrous, velvety ap pearance. THE SPIDER HOLDS HER TRAPDOOR SHUT I had difficulty in raising the door; the owner of the nest strenuously objected! The spider had placed her two fangs in the holes she had made in the under side of the lid and, bracing herself, held on for dear life. Even after my superior strength had overcome hers, she allowed herself to be lifted partly out of her nest before she let go and dropped back into the dark in terior. As soon as I let the door snap into place, she returned and got another grip. This chance meeting was the beginning of my close association with Francis Beck, who for 13 years has studied the habits of the common California trapdoor spider (Bothriocyrtum californicum). So deeply interested was I with the specimen shown me that I gladly accepted his invitation to inspect his collection. I found him working at his home next day under the trees, where he had placed in a natural setting the many specimens which he had brought from the neighbor- ing hills. Here, in boxes of adobe soil, I saw big spiders, little spiders, young and old, in dozens of "transplanted" nests. There were several hundred young ones, which had been hatched during their pa rents' captivity from eggs contained in the nests at the time of their removal (see illustration, page 197). Ever alert and watchful, trapdoor spiders are extremely sensitive to the vibrations of insects as they walk over the ground or moss. They seem to know the right instant to raise the door, spring out, and make a capture. Then, dropping back to the bottom of the burrow, they feast at leisure. Movement is so rapid that the insect is within the grasp of the hungry spider before the victim can escape (see illustration, page 199). Hundreds of sow bugs and other noc turnal insects relished by the spiders are captured by Mr. Beck and guided over the ground close to the doors of the nests to provide food for his charges. A trapdoor spider is careful not to let the door close behind her when she is making a capture, for the cover is difficult to reopen, once it snaps shut. The door fits so tightly in the tube that there is only a fine crack where a claw could be in serted to lift it. To forestall being locked out of her own home, the spider always leaves her hind legs and a part of her ab domen under the open door (see illustra tion, page 199). PATIENCE AND WATCHFUL WAITING REVEAL INGENIOUS NESTS Considerable patience is necessary to study the habits of trapdoor spiders. Many hours of watchful waiting and sometimes whole nights pass without even a glimpse of a wary spider. It is discouraging to sit in a cramped position for hours, with eyes concentrated on a particular trapdoor, only to discover that this is one of the nights the spider is not inclined to labor. On many occasions we have returned home after tramping for miles over good spider territory without finding a single nest, so cleverly are they hidden.