Silkworm Spinning and Cocoon

The transformation of a silkworm into a moth begins with the remarkable process of spinning a cocoon, a complex and fascinating biological feat. This article delves into the intricate stages of this process, exploring the silkworm’s physiological preparation and the detailed steps of cocoon construction.

1. Silk Production and Storage in the Silkworm

The silkworm’s journey to cocoon creation is fueled by specialized silk glands. These glands produce the raw materials – fibroin and sericin – essential for cocoon formation.

The silkworm accumulates the majority of its silk protein – roughly 80% – before the cocooning process begins. The remaining 20% is synthesized from body protein after cocooning starts. This shows that the silkworm efficiently transfers and transforms protein from its own body to form silk. Furthermore, silk fibroin is synthesized during the latter half of the silkworm’s fifth instar stage, while sericin is synthesized during the former half. Before actually starting to spin the cocoon, the silkworm expels the contents of its digestive tract. This preparation helps the insect focus on silk production.

2. Preparation and Initial Structure

Before fully forming the cocoon, the silkworm undergoes a preparation phase. This involves finding a suitable spot and building initial support structures.

• Cocoon Support: The silkworm first spins and attaches silk to form a basic framework, or support, for the cocoon.
• Cocoon Net: Following the support structure, the silkworm spins a loose, net-like structure on the support. This net forms the first layers of the cocoon.
• Cocoon Clothes: The silkworm then creates a thicker layer of loose silk loops on the inner surface of the cocoon net. This is the “cocoon clothes” and marks the point where the cocoon’s outline starts to take shape.

3. Spinning the Cocoon Layers

With the outline established, the silkworm begins the main stage of cocoon construction. The silk is spun in specific patterns to build the cocoon layers.

• Figure-Eight Pattern: The silkworm starts spinning silk in a “~” shape, then evolves into an “∞” shape around the inner cavity of the cocoon.
• Cocoon Pieces: Each “∞” shaped silk loop is about 1-2mm long. A group of 15-25 loops is spun as one “cocoon piece.” The silkworm moves around inside the forming cocoon, creating these pieces systematically.
• Layer Formation: As the silkworm continues to produce cocoon pieces, these layers gradually build up the cocoon’s structure. The silkworm moves, shifting positions to create each new piece.
• Pupal Lining: Lastly, the silkworm spins a thin and very soft lining in the innermost layer of the cocoon.

4. Completion of the Cocoon and Pupation

The final phase of the cocoon-making process is marked by the silkworm’s diminishing energy and slight changes in behavior.

• Reduced Activity: As the silkworm expends its energy, its body shrinks, its head movements slow, and its silk spinning becomes less rhythmic.
• Soft Cocoon Top: The silkworm orients itself with its head facing up, and its tail facing down. It then expels the remaining silk to form a soft top to the cocoon, finalizing the cocoon structure.
• Pupation: With the cocoon complete, the silkworm is now protected inside to undergo its metamorphosis. It transforms into a pupa and later, a moth, to continue its life cycle.

The spinning of a cocoon by a silkworm is a complex, multi-stage biological process. The precise execution of each step, from the production of silk proteins to the careful construction of cocoon layers, underscores the silkworm’s remarkable adaptation for survival and transformation. Companies like PandaSilk recognize the value of this process, utilizing the silk produced by these amazing insects to create high-quality silk products.