National Geographic : 1951 Jul
Spain's Silkworm Gut BY Luis MARDEN W HEN Don Quixote, Spain's mad hero, started his knightly adventures, he and Sancho Panza were riding along a road in La Mancha.* "After they had gone a couple of miles," Cervantes wrote, "Don Quixote caught sight of what appeared to be a great throng of people, who, as was afterward learned, were certain merchants of Toledo on their way to Murcia to purchase silk." In 1605, Don Quixote's publication date, Murcia was already famous for its thread silk. It took an accident to establish a new and unusual silk product-silkworm gut. A Discovery by Ragpickers The story goes that, more than a century ago, a Murcian tossed off-size worms on a refuse heap. Strolling ragpickers, curious to examine the silk-producing mechanism, tore one open. Experimenting, they stretched its two gelatinous silk glands into long threads of tough, translucent silk. So was a new industry born. Since that time Murcia has supplied the world with this filament. Some 20 plants, making gut and fishing equipment, place Murcia in competition with Redditch, Eng land's famed tackle town. In peak times Spain turns out 90,000,000 strands of gut a year. Lately, artificial sub stitutes have reduced gut exports sharply. Fishermen, who buy 70 percent of all gut, use it to conceal the connection between lines and lures (page 108). Surgeons, taking the remainder, employ it to sew wounds. Both anglers and doctors once used horse hair. Some English fishermen still prefer white horsehair, and plastic surgeons occasion ally sew with horsehair sutures. But just as the silkworm took the place of the horse, so nylon, product of the labora tory, now pushes the silkworm into the back ground. In similar fashion, nylon put the bristle hog out of the toothbrush business. Moth Undergoes Three Transformations Bombyx mori, the silkworm moth, has a four-stage life cycle: egg, larva, pupa, and imago, or mature moth.t In the thread-silk industry, sericulturists kill the insect in its cocoon or pupal stage. Then they unwind the cocoon's thread and spin the filaments into raw silk. Gut makers, eliminating the cocoon stage, stop development one step earlier. As the worms prepare to spin their silken chambers, they are killed and cured in an acid solu tion. Then the two silk glands are removed and stretched into filaments (page 105). Gut making is woman's work. Murcia farmwives buy silkworm eggs from breeders in autumn and keep them chilled until spring. On the first Friday in March they take the eggs to church to be blessed. Most growers incubate the worms between folds of cloth, but some farm women hatch them in bags hung between their breasts. Now the Spanish Government is introducing oil-burning incubators. When the minuscule worms hatch out, they begin a mulberry-leaf feast which they inter rupt only for four moltings (page 102). Finally, in three to five weeks, the worms, now grown to three inches, stop eating and prepare to spin cocoons. At this precise moment they are tossed into the lethal bath. Each Murcia family has its own formula for the pickling. Some use beer and water, others vinegar and water, or vinegar and salt. One woman's recipe: "Add salt to vinegar until an egg will float three-quarters submerged." Chickens Snap Up the Leavings Old women draw the gut (page 104). Open ing a pickled worm, the farmwife removes the silk sacs and tosses the looted carcass to a circle of eager chickens. Now, with one swift movement, she pulls the two sacs to their full length, 8 to 18 inches. When she has stretched several hundred filaments, she washes the bundles and finger-combs the strands (page 106). Finally the gut is dried in the hot sun (page 107). This raw product goes to processing plants in bundles resembling carroty wigs. The breaking point of most gut varies between 3 and 17 pounds. For more delicate, almost invisible, sizes, processors draw strands through pierced-diamond dies. Some of the finest measure three thousandths of an inch; they snap under a few ounces' strain. Though nylon has the advantages of con tinuous length, exact, uniform diameter, and dry flexibility, many expert anglers prefer gut. It remains supple in icy water and it sinks more readily than nylon. Thus a fu ture seems assured for Spain's strange in dustry. * See "Speaking of Spain," by Luis Marden, NA TIONAL GEOGRAPHIC MAGAZINE, April, 1950. t See "Strange Habits of Familiar Moths and But terflies," by William Joseph Showalter, NATIONAL GEOGRAPHIC MAGAZINE, July, 1927.