Life Cycle of the Silkworm (Bombyx Mori)

Classification
Phylum: Arthropoda
Class: Insecta
Sub-Class: Pterygota
Division: Endopterygota
Order: Lepodoptera
Genus: Bombyx
Species: mori

Various life cycle stages of the silkworm are egg, larva, pupa, and adult male and female.

Egg
Females lays 300–500 eggs in clusters upon mulberry leaves.

Larva
The egg hatches into a larva known as the caterpillar larva. It is 6-mm long, rough and wrinkled, with a whitish or grayish body made of 12 segments. The head bears mandibulate mouthparts. The thorax has 3 pairs of jointed true legs. The abdomen has 5 pairs of unjointed, stumpy pseudolegs. When the color of larvae heads turns darker, it means that it is time for them to molt. After they have moulted four times, their bodies turn slightly yellow and their skin becomes tighter. The larvae enclose themselves in a cocoon of raw silk produced in the salivary glands that provides protection during the vulnerable, almost motionless pupal state.

Pupa
Within a fortnight the caterpillar larva inside the cocoon becomes a pupa or chrysalis. Its body becomes shortened. Silk threads wrap around the body of the larva to give rise to a cocoon.

Adult
In 3 or 4 months, the pupa metamorphoses into adult. A single egg develops into either a male or a female. Males are smaller than females. Males die after copulation and females die after laying eggs. Stages of Silkworm in Detail

Egg
Soon after fertilization, each female lays about 300–500 eggs in clusters upon the leaves of the mulberry tree. The female covers the eggs with a gelatinous secretion, which sticks them to the leaves. The small, smooth, and spherical eggs are first yellowish-white, and become darker later on. In tropical countries, the silk moth lays nondiapause eggs, which enable them to raise 2 to 7 generations within a year. In temperate countries, diapause eggs are laid, so that a single generation is produced per year.

Larva
The silkworm, which hatches from the egg, is known as the caterpillar. It is a tiny creature about 6-mm long, and moves about in a characteristic looping manner.

Head
The head has mandibulate mouthparts.

Thorax
It has 3 distinct segments with 3 pairs of jointed true legs.

Abdomen
It is segmented into 10 parts, with 5 pairs of unjointed, stumpy pseudolegs, a short dorsal and horn on the eighth segment, and a series of respiratory spiracles, or ostia, on either lateral side.

Pupa
It is also known as the chrysalis. The caterpillar stops feeding and returns to a corner among the leaves. It begins to secrete the sticky fluid of its salivary glands through a narrow pore, called the spinneret. The sticky substance turns into a fine, long, and solid thread of silk. The thread becomes wrapped around the body of the caterpillar, forming a pupal case or covering known as the cocoon. Within a fortnight, the silkworm transforms into a tubular brownish organism, the pupa or chrysalis.

Adult
The adult moth is about 25-mm long with a wing size of 40–50 mm. It is robust and creamy white in color. The body is divided into 3 portions, i.e., head, thorax, and abdomen.

Head
The heads has a pair of compound eyes, a pair of branched or plumed antennae, and the mandibulate mouth part.

Thorax
The thorax has 3 pairs of legs and 2 pairs of wings. The cream-colored wings are about 25-mm long, and are marked by several faint or brown lines.

Abdomen
The abdomen consists of 10 segments.