Silkworms are not worms. Silkworm gut has nothing to do with intestines. Every angler knows what a worm is. Worms neither have legs nor spin cocoons. Silkworms are the larvae-caterpillars--of the moth Bombyx mori. If allowed to pupate the larva will spin a cocoon of fine thread from which we get some grand flosses, but that is another tale.

Silkworm gut is made from a modified salivary gland (each larva has two) which is connected to an opening in the critter's lower lip. These glands are filled with a viscous fluid that hardens upon exposure to air. Again, if the larva is allowed to pupate, it would spin its silken cocoon from this fluid. Silkworm gut does not come out of a silkworm's intestine; frass (dried larval-insect excrement--your word for the day) comes out of a silkworm’s intestine.

By the way, silkworm pupae are eaten in many areas where silk is produced. The cocoons are immersed in boiling water or heated in ovens to kill the pupae. The pupae are then eaten by workers as the silk is unwound. The pupae contain 23 percent protein, 14 percent fat, and 2 calories per gram (for comparison, beef has 18 percent protein, 21 percent fat, and 2.6 calories per gram).

The center of silkworm-gut production was the town of Murcia in southeastern Spain. The silkworms were fed mulberry leaves until they reached maturity, at about three inches in length. The mature larvae were plunged into a vinegar bath. The insect was slit open, the glands removed, and each gland pulled across the worker's knees, stretching them to full length. Each gland resulted in a certain length and thickness of gut. The puller could not control these variables. The raw gut was then boiled in soapy water to remove the yellow coating (the walls of the gland) from the strands. After rinsing and drying in the sun the strands were sorted for size and quality. Thickness was necessarily a subjective determination as the strands tapered toward both ends. Length was determined by using an instrument called a lata. The lata contained twenty-four measurements from seven to eighteen and one-half inches. Gut over seveteen inches was uncommon and the lata itself stopped shy of nineteen. Beware of claims that twisted silkworm gut can be had in lengths of twenty-four inches. The gut was classified by quality into, from high to low, Selecta, Superior, and Estriada.

Next came a series of manipulations designed to improve the appearance of the gut. It was put into bundles of one hundred strands. The ends of ten to twelve bundles were clamped in two vises which could be pulled apart. While under tension between the vises the strands were rubbed vigorously with chamois leather, resulting in straighter strands. Gut in the lower grades could be improved by a process called Mazantining. The strands were moistened, then rubbed with a dry linen cloth. This removed slight defects and to a limited extent thinned the gut. The entire process, from raw gut to finished product, took four to six weeks.

Natural gut was seldom thinner than 2X (.009 inch). If finer gut was desired it was drawn. The drawing process was done in England. One gut end was given a point by rubbing it with a mixture of water and abrasive. The pointed end was inserted into a die, which consisted of a metal plate measuring three and one-half by one inches and upon which were mounted a number of jewels bored with holes. The protruding end was then grasped by pliers and the entire strand pulled through. Finer thicknesses were produced by pulling the gut through successively smaller holes.

The following chart, from Ernest Schwiebert's Trout, compares the various sizes of gut. Keep in mind that, except for drawn gut, thickness was not uniform. Additionally, some firms were accused of exaggerating the strength of their gut by, for example, labeling .008 strands as 4X.