The silkworm

What do you know about silk?
Silk is a natural fiber composed of proteins (fibroin). Although several groups of arthropods produce silk threads, only the one made by Bombyx mori L. caterpillars (a moth of Chinese origin, from the Family Bombycidae) is currently used in the textile industry worldwide.

The silkworm

Bombyx mori caterpillars, commonly known as “silkworms”, hatch in late winter or early spring, which coincides with the appearance of mulberry leaves (Morus spp.), their only food. Their chalk-white or slightly yellowish color makes them not stand out. It takes them about 35 days to go from being newly born to weaving their cocoon, and they spend most of that time feeding. During their lifetime caterpillars molt 6 times, which allows them to grow from the 4 millimeters with which they hatch up to 8 centimeters.

Silk moths

Silk moth adults are relatively small, white or creamy colored, and although they have wings they are unable to fly. They have atrophied mouthparts, so they do not eat and their life is very short, about 5 to 7 days. The only function of adults is to reproduce. As soon as they emerge from the cocoon and their wings are stretched and dried, males use their large pectinate antennae (in the shape of a comb) to perceive the scent trail of females and find a mate. After being fecundated, the females leave between 300 and 500 eggs glued to any surface. The eggs are yellow at the beginning and later turn gray, indicating that the embryo has begun to develop.

Silk cocoons

At the end of its growth, each caterpillar of Bombyx mori weaves a cocoon around itself with a silk thread that comes out of its mouth through an organ called spinneret. The caterpillar also produces sericin, a substance that sticks together the different coils of the thread. Inside the cocoon the larva will molt for the last time, giving rise to the pupa or chrysalis, where the most spectacular part of the metamorphosis will take place: its transformation into a winged adult.

Obtaining silk

The breeding of the «silkworm» and its textile use goes back to 3400 years BC. Since then, the species has been subjected to artificial selection in order to obtain better quality silk and no longer exists in nature, only in human-made hatcheries. For their use in the industry, cocoons are subjected to steam and dried in stoves ten days after being knitted by the caterpillars. Subsequently, they are submerged in hot water and special machines carefully unwound the thread to recover it whole. The fabrics made with these threads are very valuable, and at some point in time they were more valuable than gold. In each hatchery, some cocoons are separated and taken care of until the adults destined to produce the next generation of caterpillars emerge, in order to continue production.

Argentine silk

Humans also use other types of silks that exist in different parts of the world, many produced by moth or butterfly caterpillars and spiders. In Argentina, the silk of moths of the genus Rothschildia, known as «Windowed Moths» (Family Saturnidae), is used in the manufacturing of handmade textiles that have a color and a quality similar to that of the fiber of camelids like guanaco, llama, and alpaca. The techniques for obtaining this silk have been known for centuries and used by few people, generally of advanced age, in the mountains of the province of Catamarca.

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2020 Desarrollado por Centro de Cómputos Facultad de Ciencias Exactas, Físicas y Naturales